The one-pot conversion of ethanol to butadiene is a promising route for butadiene production; however, simultaneous attainment of high butadiene productivity and high butadiene selectivity is challenging. Here, zeolite-confined bicomponent Zn–Y clusters were constructed and applied as robust catalysts for ethanol-to-butadiene conversion with a state-of-the-art butadiene productivity of 2.33 gBD/gcat/h and butadiene selectivity of ∼63%. Structural confinement effects are responsible for the enhanced butadiene production efficiency via a multiple-step cascade reaction.Keywords: cascade reaction; catalysis; confinement effects; ethanol-to-butadiene; zeolite;

A direct hydrothermal synthesis approach to Fe/ZSM-5 zeolites was developed by using a ferric complex, i.e. ethylenediaminetetraacetic acid ferric sodium (EDTA-FeNa), as both an iron source and a structure-directing agent. During the hydrothermal synthesis, EDTA-FeNa complexes were encapsulated within zeolite channels of ZSM-5 and they underwent transformation to highly dispersed extraframework iron species, i.e. isolated ferric ions and oligomeric FexOy clusters, upon calcination removal of organic species. The as-prepared Fe/ZSM-5 zeolites could be established as bi-functional catalysts containing both acid sites and iron sites. As expected, the as-prepared Fe/ZSM-5 zeolites exhibited remarkable catalytic activity in the selective reduction of nitrogen oxides by ammonia (NH3-SCR), with a nitrogen oxide conversion of >99% in a wide temperature range of 573–693 K under simulated industrial conditions. Meanwhile, good stability and tolerance to water vapor and sulfur dioxide could be achieved, making these Fe/ZSM-5 zeolites promising candidates for practical application. In contrast to conventional post-synthesis modification approaches to Fe/ZSM-5, the one-pot hydrothermal synthesis approach appeared to be very simple and easily reproducible, and the formation of inactive iron oxide nanoparticles can be completely avoided, which accordingly leads to high NH3-SCR activity.

•Ru/TiO2 as a robust catalyst for the deoxygenation of stearic acid under mild conditions.•Large metallic ruthenium particles with weak metal-support interaction established as preferred active sites for deoxygenation.•Stearic acid deoxygenation pathway constructed via the combination of experimental observations and theoretical calculations.Triglycerides represent a type of sustainable energy source and robust catalysts for triglycerides refining to biofuels are very challenging. Herein, we report supported ruthenium catalysts, optimized from group VIII metal catalysts, for the selective conversion of triglycerides to diesel-range alkanes under mild conditions. The catalyst supports and ruthenium loadings show significant impacts on the performance of ruthenium catalysts, and Ru/TiO2 with ruthenium weight loading of 1.68% is optimized for the reaction. Typically, the platform compound stearic acid could be directly converted, or via 1-octadecanol as an intermediate product, to n-heptadecane and n-octadecane in n-heptane solvent using the optimized Ru/TiO2 catalyst at 473 K and under 3 MPa H2. On the basis of catalytic and spectroscopic characterization results, large ruthenium metal particles are established as the preferred active sites for stearic acid conversion. The complete reaction network of stearic acid deoxygenation on flat Ru (0001) is investigated by theoretical calculations. It is revealed that different pathways run simultaneously during the reaction and the adsorbed acyl species C17H35CO* are the key reaction intermediates for the catalytic deoxygenation on Ru (0001). The removal of adsorbed CO by hydrogenation is the rate-controlling step contributing to the highest energy barrier within the reaction network.Download high-res image (182KB)Download full-size image

WO2.72 nanoparticles with sizes below 10 nm have been synthesized via controllable alcoholysis followed by thermal treatment. Through an in situ loading process, homogeneous composites containing WO2.72 nanoparticles and reduced graphene oxide, i.e. WO2.72/RGO, can be fabricated. The physico-chemical properties of the as-prepared WO2.72 and WO2.72/RGO composites are investigated by means of XRD, Raman, XPS, TGA, SEM, TEM and UV-vis spectroscopy. The RGO support, as a very good electron conductor, can efficiently transfer the photo-generated electrons formed on WO2.72 and suppress their recombination. As a result, WO2.72/RGO nano-composites exhibit remarkable photocatalytic activity in both the oxygen evolution from water splitting and selective oxidation of benzyl alcohol, several times higher than pristine WO2.72. The better light harvesting properties of WO2.72/RGO nano-composites than WO2.72 nanoparticles can be directly demonstrated by photocurrent response analysis.

The synthesis of gallium oxide and nitride nanocrystals is challenging. Herein, a forced hydrolysis route is developed to synthesize α-GaOOH and the morphology control of nanocrystals is realized by adjusting the ratios of ionic strength in the synthesis system. The as-prepared α-GaOOH nanorods can be transformed into α-Ga2O3 nanorods upon calcination and can be further transformed into GaN nanocrystal assemblies through nitridation at elevated temperatures, which provides a top-down strategy to gallium oxide and nitride nanocrystals. The synthesis results are investigated by means of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The optical properties, i.e. ultra-violet visible absorption (UV-vis) and photoluminescence, of as-obtained α-Ga2O3 nanocrystals with different morphologies are examined and the morphology–property relationship is discussed.

Low-silica AlPO-34 materials with similar crystal sizes but different Brønsted acid site densities were prepared and investigated as catalysts in methanol-to-olefin (MTO) conversion. The effect of Brønsted acid site density on catalyst activity and the dominant reaction mechanism during the MTO conversion was investigated via TGA, GC-MS, solid-state NMR spectroscopy, and in situ UV/vis spectroscopy together with the catalytic performance. For the catalysts with lower Brønsted acid site densities, the olefin-based cycle mechanism is the dominant mechanism during the MTO conversion. Long-chain alkenes, e.g., C5–C6 alkenes, act as intermediates that are cracked to lower olefins, or are converted to dienes via hydride transfer reactions, and can also diffuse out of the cages of low-silica AlPO-34 catalysts as the products. With decreasing Brønsted acid site density or reaction temperature, the methylation route of the olefin-based cycle was found to be much more favored than the cracking route. Therefore, a higher selectivity to C5–C6 alkenes (∼50%) is achieved. Simultaneously, dienes are the predominant deposits occluded in the used catalysts. For catalysts with slightly higher Brønsted acid site densities, the long-chain alkenes are rapidly transformed to aromatics and, subsequently, an aromatic-based cycle mechanism contributes to the MTO conversion. Interestingly, the catalyst with the most suitable Brønsted acid site density can well balance the above-mentioned two reaction cycles accompanied by a low deactivation rate, leading to a long catalyst lifetime of up to 15 h.

•A single zeolite Meso-Zr-Al-beta containing Brønsted acid sites, Lewis acid sites and mesopores successfully constructed.•Meso-Zr-Al-beta with multifunctional sites as a robust catalyst for cascade reactions in biomass valorization.•A single zeolite catalyst containing multifunctional sites is better than combination catalyst systems.Hierarchical Meso-Zr-Al-beta zeolites are successfully prepared through a multiple-step post-synthesis strategy composed of controlled dealumination, desilicication and metal incorporation. The presence of both Brønsted and Lewis acid sites with a certain extent of strength in Meso-Zr-Al-beta is demonstrated by NH3-TPD and FTIR spectroscopy with pyridine adsorption/desorption. The creation of mesopores via desilicication through alkaline treatment is confirmed by N2 adsorption/desorption isotherms. Meso-Zr-Al-beta, with Brønsted acid sites, Lewis acid sites and mesopores, is applied as a zeolite catalyst for the cascade conversion of biomass platform molecule furfural to γ-valerolactone. Owing to the presence of multiple functional sites and their mutual compatibility, remarkable activity for γ-valerolactone production and catalyst recyclability could be achieved with a single Meso-Zr-Al-beta, which appears to be a better catalyst than the commonly-employed combination catalyst systems. The multifunctional Meso-Zr-Al-beta zeolite is also applied as a promising catalyst in other cascade reactions in biomass valorization, i.e. glucose conversion to 5-hydromethylfurfural and trioses conversion to ethyl lactate. Similar zeolite catalysts containing multiple functional sites could be prepared via similar routes, and the number of acid sites and their strength can be adjusted to some extent to derive an optimized catalyst by changing the preparation parameters.Download high-res image (128KB)Download full-size image

•Ni/NiO composite as a robust catalyst for the hydrogenation of levulinic acid to γ-valerolactone.•Partial reduction of nickel oxide in hydrogen results in the formation of Ni/NiO heterojunctions.•A cooperative Langmuir-Hinshelwood mechanism proposed for levulinic acid hydrogenation on Ni/NiO heterojunctions.A non-precious metal catalyst Ni/NiO is developed for the efficient hydrogenation of levulinic acid to γ-valerolactone under mild conditions. Treating nickel oxide in hydrogen at controlled temperature of 473–573 K results in its partial reduction to metallic nickel and the formation of Ni/NiO heterojunctions, as indicated by the characterization results from in situ XRD, XPS and TEM. The as-prepared Ni/NiO catalyst exhibits remarkable activity in levulinic acid hydrogenation with a high mass activity of 14.1 mmol/h/g at 393 K, being over 18 times higher than NiO and 10 times higher than metallic Ni. Besides, Ni/NiO shows very good stability and recyclability during the reaction, making it a promising catalyst for practical levulinic acid hydrogenation. The formation of Ni/NiO heterojunctions is crucial for the remarkable activity of Ni/NiO composite catalyst and a cooperative Langmuir-Hinshelwood mechanism is proposed for levulinic acid hydrogenation on the basis of kinetic analysis and theoretical calculations. The concept of cooperative catalysis on metal/oxide heterojunctions can be expanded to other hydrogenation reactions.Download high-res image (149KB)Download full-size image

We report a heterogeneous catalysis strategy to the sustainable hydration of epoxides by designing robust Lewis acid catalysts confined in zeolite cages as natural shape-selective nanoreactors. In the case of ethylene oxide hydration, Sn-H-SSZ-13 zeolite exhibits remarkable catalytic performance, with an ethylene oxide conversion above 99% and a monoethylene glycol selectivity above 99%, at approaching stoichiometric water/ethylene oxide ratios and near-ambient reaction temperatures. It is revealed by theoretical studies that partially hydroxylated Sn species are the preferred Lewis acid sites for the hydration of ethylene oxide. The concept of Lewis acid catalysis confined in zeolite cages may be applied in the future in the chemical industry to develop energy-saving and environmentally benign processes.Keywords: epoxide hydration; Lewis acid catalysis; partially hydroxylated Sn species; shape-selective; Sn-H-SSZ-13

The selective scission of chemical bonds is always of great significance in organic chemistry. The cleavage of strong carbon–carbon σ bonds in the unstrained systems remains challenging. Here, we report the selective hydrogenolysis of carbon–carbon σ bonds in primary aliphatic alcohols catalyzed by supported metals under relatively mild conditions. In the case of 1-hexadecanol hydrogenolysis over Ru/TiO2 as a model reaction system, the selective scission of carbon–carbon bonds over carbon–oxygen bonds is observed, resulting in n-pentadecane as the dominant product with a small quantity of n-hexadecane. Theoretical calculations reveal that the 1-hexadecanol hydrogenolysis on flat Ru (0001) undergoes two parallel pathways: i.e. carbon–carbon bond scission to produce n-pentadecane and carbon–oxygen bond scission to produce n-hexadecane. The removal of adsorbed CO on a flat Ru (0001) surface is a crucial step for the 1-hexadecanol hydrogenolysis. It contributes to the largest energy barrier in n-pentadecane production and also retards the rate for n-hexadecane production by covering the active Ru (0001) surface. The knowledge presented in this work has significance not just for a fundamental understanding of strong carbon–carbon σ bond scission but also for practical biomass conversion to fuels and chemical feedstocks.Keywords: carbon−carbon bond scission; hydrogenolysis; primary aliphatic alcohols; ruthenium catalyst; theoretical calculations

Little is known on the early stages of the methanol-to-olefin (MTO) conversion over H-SAPO-34, before the steady-state with highly active polymethylbenzenium cations as most important intermediates is reached. In this work, the formation and evolution of carbenium ions during the early stages of the MTO conversion on a H-SAPO-34 model catalyst were clarified via 1H MAS NMR and 13C MAS NMR. Several initial species (i.e., three-ring compounds, dienes, polymethylcyclopentenyl, and polymethylcyclohexenyl cations) were, for the first time, directly verified during the MTO conversion. Their detailed evolution network was established from theoretical calculations. On the basis of these results, an olefin-based catalytic cycle is proposed to be the primary reaction pathway during the early stages of the MTO reaction over H-SAPO-34. After that, an aromatic-based cycle may be involved in the MTO conversion for long times on stream.Keywords: density functional theory calculation; dual cycle mechanism; H-SAPO-34; methanol-to-olefin conversion; polymethylcyclohexenyl cations; polymethylcyclopentenyl cations

Mesoporous zirconosilicate, stannosilicate, and titanosilicate with the BEA structure framework have been prepared from the commercially available Beta zeolite via acid–alkaline treatments and subsequent dry impregnation of appropriate organometallic precursors. N2 adsorption–desorption isotherms and TEM observations confirm that alkaline treatment can induce desilication to create intra-crystalline mesopores from the partially dealuminated Beta sample. The incorporation of Zr species into the zeolite framework at formed silanol defect sites is monitored by infrared and 1H MAS NMR spectroscopy. Characterization results from UV-vis and XPS reveal that the majority of the incorporated Zr species exist in the form of tetrahedral Zr(IV) in the zeolite framework. The creation of Lewis acid sites with moderate acid strength upon Zr incorporation is confirmed by FTIR spectroscopy with pyridine adsorption. The as-prepared mesoporous Zr-Beta exhibits a remarkable catalytic activity and regio-selectivity to β-amino alcohols in the ring-opening aminolysis of epoxides, and the presence of mesopores can promote the reaction to a great extent through enhanced mass transfer. The impacts of the Lewis acidity of the catalysts, the basicity of amines and adsorption of reactants on the ring-opening aminolysis of epoxides are discussed in detail.

A facile fast hydrolysis route to a three-dimensional flow-like iron doped rutile TiO2 nanostructure is developed. With iron species doping into both the bulk phase and the surface, the bandgap narrowing of rutile TiO2 is realized and the dissociative adsorption of water on the surface is promoted, which accordingly lead to greatly enhanced activity in visible-light-driven water oxidation.

With ethanol as a probe molecule, the surface sites of anatase and rutile can be distinguished using 13C CP/MAS NMR spectroscopy, which offers an opportunity to investigate the transfer of photo-induced electrons from rutile to anatase in the mixed-phase TiO2.

The formation and evolution of initial reaction intermediates as well as the reaction mechanism during the early period of the methanol conversion on the silicoaluminophosphate SAPO-41 with one-dimensional and 10-numbered ring pore system was elucidated. According to in situ UV–vis spectroscopy, the formation and nature of intermediates formed on the catalysts in the methanol conversion process were monitored. The intermediates remaining on the catalysts after quenching the methanol conversion were determined by ex situ UV–vis, 1H MAS NMR, and 13C MAS NMR spectroscopy, and the reactivity of these species was investigated by adsorption of ammonia and subsequent solid-state NMR spectroscopy. The above-mentioned spectroscopic studies gave a detailed mechanistic insight into the induction period of the methanol conversion on SAPO-41. Monoenylic carbenium ions, being the dominating species during the initial period of the methanol conversion, were rapidly formed and gradually transferred to dienylic carbenium ions, benzene-based carbenium ions, and trienylic carbenium ions, in addition to three-ring compounds and dienes with different chain lengths. On the basis of these spectroscopic observations and the catalytic results, the olefin-based reaction cycle is disclosed to be the dominating reaction mechanism in the initial period of the methanol conversion on SAPO-41.

Nanocrystalline Sn-Beta zeolites have been successfully prepared via an improved two-step postsynthesis strategy, which consists of creating vacant T sites with associated silanol groups by dealumination of parent H-Beta and subsequent dry impregnation of the resulting Si-Beta with organometallic dimethyltin dichloride. Characterization results from UV–vis, XPS, Raman, and 119Sn solid-state MAS NMR reveal that most Sn species have been successfully incorporated into the framework of Beta zeolite through the postsynthesis process and exist as isolated tetrahedral Sn(IV) in open arrangement. The creation of strong Lewis acid sites upon Sn incorporation is confirmed by FTIR spectroscopy with pyridine adsorption. The Sn-Beta Lewis acid catalysts are applied in the ring-opening hydration of epoxides to the corresponding 1,2-diols under near ambient and solvent-free conditions, and remarkable activity can be obtained. The impacts of Lewis acidity, preparation parameters, and reaction conditions on the catalytic performance of Sn-Beta zeolites are discussed in detail.Keywords: epoxide; organometallic; postsynthesis; ring-opening hydration; Sn-Beta

Ti-Beta zeolite has been successfully prepared via a reproducible and scalable two-step post-synthesis strategy, which consists of creating vacant T sites with associated silanol groups by dealumination of H-Beta and subsequent dry impregnation of the resulting Si-Beta with titanocene dichloride. The mechanism of Ti incorporation into the framework of Beta is investigated by diffuse reflectance infrared Fourier transform (DRIFT) and multinuclear solid-state nuclear magnetic resonance (SSNMR) spectroscopy. Characterization results obtained from diffuse reflectance ultraviolet-visible (UV-vis) and X-ray photoelectron spectroscopy (XPS) reveal that the majority of incorporated Ti species exist in the form of isolated tetrahedrally coordinated Ti(IV) in the zeolite framework while a minority exists in the form of isolated octahedrally coordinated Ti(VI) at framework or extra-framework positions. The obtained Ti-Beta zeolites are highly active and selective catalysts for the epoxidation of unsaturated ketones, e.g. 2-cyclohexen-1-one, with hydrogen peroxide as an oxidant. A quasilinear correlation between the epoxidation rate and the number of framework Ti(IV) species could be drawn evidencing that these Ti(IV) species are responsible for the epoxidation activity of the Ti-Beta zeolites under study. The impact of preparation parameters and reaction conditions on the catalytic performances of the Ti-Beta zeolites in the epoxidation of unsaturated organic compounds with hydrogen peroxide is discussed in detail.

A one-step hydrothermal route is developed to prepare amino-grafted graphene oxide as an environmentally benign heterogeneous solid base catalyst.

In the present work, the mechanism of the methanol-to-hydrocarbon (MTH) conversion over the silicoaluminophosphate SAPO-41 with one-dimensional 10-ring pores has been investigated. For this purpose, catalytic experiments with co-feeding of reactants, in situ FTIR and UV/Vis spectroscopy, and 1H MAS NMR spectroscopy of used catalysts upon loading of ammonia were performed. Using these methods, only a low content of aromatics could be observed on the working SAPO-41 catalyst. These findings and the characteristic changes in the ethene selectivity during the co-feeding experiments indicate that alkylaromatics can be excluded as active hydrocarbon pool compounds on SAPO-41 applied as MTH catalysts. On the other hand, dienes and enylic carbenium ions were detected using FTIR and UV/Vis spectroscopy and the formation of amines by reaction of alkenes with ammonia was detected via1H MAS NMR spectroscopy. These results are experimental evidence that large olefins partially existing in their carbenium state dominate the catalytically active hydrocarbon pool on the working SAPO-41. Due to this dominant alkene-based reaction mechanism and the limited formation of aromatics, SAPO-41 is a suitable catalyst for the C3+C4 olefin as well as gasoline production.

•Available Fe–O–Al species accounts for 60% of total iron in Fe-ZSM-5.•Chemisorbed oxygen species react with gaseous propane to produce propylene via Eley–Rideal mechanism.•Formation of large alkylbenzene inside zeolite channels leads to catalytic deactivation.•Deactivation behavior of Fe-ZSM-5 in ODHP with nitrous oxide strongly depends on N2O/C3H8 ratio.Fe-ZSM-5 was prepared via solid-state exchange method using ferrocene as iron precursor and applied as a model catalyst to investigate the reaction and deactivation mechanisms of the oxidative dehydrogenation of propane (ODHP) with nitrous oxide. Characterization results reveal that after severe calcination highly isolated Fe–O–Al species are the only exposed iron sites detectable, which account for ca. 60% of the total iron species in Fe-ZSM-5. Results from temperature-programmed experiments and in situ DRIFT spectroscopy suggest that the chemisorption of nitrous oxide on Fe–O–Al species leads to the formation of stable mono-oxygen species, which can react with gaseous propane to produce propylene with high selectivity. The accumulation of organic species in the catalyst is observed during the reaction, and the major organic species are determined to be alkylbenzenes. The accumulation rate and the specific constitution of alkylbenzenes are found to depend on the relative partial pressures of propane and nitrous oxide: lower N2O/C3H8 ratios result in formation of aromatics with smaller kinetic diameter, which are accumulated at a lower rate. This leads to lower deactivation rates and longer catalyst lifetimes. Remarkably, a superior stable propane conversion rate of ca. 13 mmol gcat−1 h−1 and a propylene production rate of ca. 6 mmol gcat−1 h−1 can be kept for >40 h with a N2O/C3H8 ratio of 1:2.

•16/17O isotope exchange (OIE) on TiO2 was studied by 17O MAS NMR.•The surface structure becomes disordered via phase transition from anatase to rutile.•TiOH groups are not involved in the OIE on dehydrated TiO2 with 17O2 gas.•The activation energy for OIE on mixed-phase TiO2 is lower than on anatase.•Distorted surface oxygen species accelerate the OIE on mixed-phase TiO2.Quantitative 17O MAS NMR investigation of the 16/17O isotope exchange on pure-anatase TiO2/A and mixed-phase TiO2/A + R with an anatase to rutile ratio of 1:1 has been performed. Evaluation of the exchange kinetics hints to a strong decrease of the activation energy of this reaction on mixed-phase TiO2/A + R material (61 (A) and 70 kJ/mol (R)) compared with pure-anatase TiO2/A (105 kJ/mol). Furthermore, a very rapid increase of the 17O MAS NMR signals of surface oxygen species indicates a preferred 16/17O isotope exchange at these sites and a subsequently exchange with 16O framework atoms in the anatase and rutile domains.Graphical abstract

SAPO-34 materials with comparable Brønsted acid site density but different crystal sizes were applied as methanol-to-olefin (MTO) catalysts to elucidate the effect of the crystal size on their deactivation behaviors. 13C HPDEC MAS NMR, FTIR, and UV/vis spectroscopy were employed to monitor the formation and nature of organic deposits, and the densities of accessible Brønsted acid sites and active hydrocarbon-pool species were studied as a function of time-on-stream (TOS) by 1H MAS NMR spectroscopy. The above-mentioned spectroscopic methods gave a very complex picture of the deactivation mechanism consisting of a number of different steps. The most important of these steps is the formation of alkyl aromatics with large alkyl chains improving at first the olefin selectivity, but hindering the reactant diffusion after longer TOS. The hindered reactant diffusion leads to a surplus of retarded olefinic reaction products in the SAPO-34 pores accompanied by their oligomerization and the formation of polycyclic aromatics. Finally, these polycyclic aromatics are responsible for a total blocking of the SAPO-34 pores, making all catalytically active sites inside the pores nonaccessible for further reactants.Keywords: benzene-based carbenium ions; Brønsted acid sites; crystal size; deactivation mechanism; in situ spectroscopy; methanol-to-olefin conversion; SAPO-34

Under UV-visible light irradiation, multiple synergetic promotion effects on the photocatalytic activity of TiO2 by gold deposition can be observed, and plasmonic Au/TiO2 shows great potential for photocatalytic solar conversion.

Fe–MFI prepared by reductive solution ion-exchange was investigated as catalyst for the oxidative dehydrogenation of propane with nitrous oxide, and a maximal propylene yield of ca. 14% could be obtained at the reaction temperature of 673 K. Accumulative acid post-treatments were performed on Fe–MFI and a gradual increase of maximal propylene yield to ca. 25% could be observed. The Fe–MFI samples before and after acid post-treatments were characterized by means of ICP, XRD, DRIFT, TEM, UV-Vis, H2-TPR, NH3-TPD and EPR. The results clearly indicated the transformation of iron species during acid post-treatments. The active iron species in Fe–MFI before and after acid post-treatments were characterized by FTIR spectra of NO adsorption. Based on the characterization and catalytic results, the extra-framework Fe–O–Al species and/or isolated iron species in Fe–MFI were proposed to be more active than oligonuclear iron species for propane dehydrogenation with nitrous oxide.

The sole effect of surface/bulk defects of TiO2 samples on their photocatalytic activity was investigated. Nano-sized anatase and rutile TiO2 were prepared by hydrothermal method and their surface/bulk defects were adjusted simply by calcination at different temperatures, i.e. 400–700 °C. High temperature calcinations induced the growth of crystalline sizes and a decrease in the surface areas, while the crystalline phase and the exposed facets were kept unchanged during calcination, as indicated by the characterization results from XRD, Raman, nitrogen adsorption–desorption, TEM and UV-Vis spectra. The existence of surface/bulk defects in calcined TiO2 samples was confirmed by photoluminescence and XPS spectra, and the surface/bulk defect ratio was quantitatively analyzed according to positron annihilation results. The photocatalytic activity of calcined TiO2 samples was evaluated in the photocatalytic reforming of methanol and the photocatalytic oxidation of α-phenethyl alcohol. Based on the characterization and catalytic results, a direct correlation between the surface specific photocatalytic activity and the surface/bulk defect density ratio could be drawn for both anatase TiO2 and rutile TiO2. The surface defects of TiO2, i.e. oxygen vacancy clusters, could promote the separation of electron–hole pairs under irradiation, and therefore, enhance the activity during photocatalytic reaction.

LaCu-ZSM-5/cordierite and Ir/ZSM-5/cordierite were prepared and studied as possible catalysts for the selective reduction of nitrogen oxides in excess oxygen. LaCu-ZSM-5/cordierite exhibited good activity in C3H6-SCR reaction and a maximal nitrogen oxide conversion of ca. 80% could be obtained at 623 K under reaction conditions employed. The existence of carbon monoxide in the reaction system showed positive effects on C3H6-SCR over LaCu-ZSM-5/cordierite. Ir/ZSM-5/cordierite exhibited good activity in CO-SCR reaction and a maximal NOx conversion of ca. 55% could be obtained at 523 K. The existence of C3H6 showed negative effects on CO–SCR over Ir/ZSM-5/cordierite at relatively low temperatures. Based on the catalytic results, combination catalyst LaCu-ZSM-5/cordierite and Ir/ZSM-5/cordierite were developed for the reduction of nitrogen oxides from real lean-burn automobile exhaust by utilizing hydrocarbons and carbon monoxide as reducing agents. With contributions from both C3H6-SCR and CO–SCR, the major pollutants in lean-burn automobile exhaust, e.g. nitrogen oxides, unburned hydrocarbons and carbon monoxide, could be purified simultaneously.Highlights► CO promotes C3H6-SCR over LaCu-ZSM-5/cordierite. ► C3H6 suppresses CO-SCR over Ir/ZSM-5/cordierite. ► Major pollutants in automobile exhaust are purified over combination catalyst.

We systematically investigated the reaction mechanism and effect of O2 on N2O reduction by NH3 over an Fe–Mordenite (MOR) catalyst. O2 has no inhibitory effect on N2O reduction, and NH3 selective catalytic reduction (SCR) of N2O is superior to NH3 oxidation by O2. We found that the mechanism of NH3 SCR of N2O involves the redox cycle of Fe(III)–OH sites, with Fe(III)–OH reduction by NH3 as the first and rate-determining step. Then N2O is activated at the reduced Fe(II)–OH sites into NO/N or N2/O, reoxidizing the Fe(II)–OH into Fe(III)–OH sites. Next, the NO formed in situ reacts with adsorbed NH2 to form NH2NO, which further decomposes to N2 and water. In addition, some NO may join with O to form NO2, which reacts with NH4+ to produce NH4NO2 and further decomposes to N2 and water. It is possible that under the steady state, N–NO breaking accounts for two-thirds of N2O splitting. The formation of NO intermediates plays a crucial role in this reaction. The structural arrangement of MOR zeolites and the high content of Fe ions provides two proximal Fe ions, that is, Fe(III)···Fe(III) pairs, as the active sites for this N–NO breaking, resulting in the high activity of Fe–MOR.Keywords: Fe−MOR catalyst; mechanism; N2O; NH3 SCR; O2 effect;

In this work, a series of phosphorus-modified HMCM-22-x%P samples are prepared by impregnation of HMCM-22 with aqueous solution of (NH4)2HPO4 and subsequent calcination. The phosphorus-modified HMCM-22 samples were characterized by means of XRD, NH3-TPD, and multinuclear (31P, 29Si, 27Al and 1H) MAS NMR techniques. The phosphorus-modified HMCM-22 samples, together with parent HMCM-22, are studied as possible catalysts for methanol-to-hydrocarbons (MTH) reaction. HMCM-22-3%P exhibits very good MTH performance and 100% methanol conversion with ca. 70% selectivity to light olefins can be achieved within time-on-stream of 40 h at 723 K. The MTH reaction over H-MCM-22 and phosphorus-modified HMCM-22 is monitored by in situ UV/Vis spectra, and the hydrocarbon pool species occluded in spent catalysts are analyzed by ex situ GC–MS spectra. Based on the characterization and catalytic results, the modification effects of phosphorus on HMCM-22 and corresponding impacts on the MTH reaction are discussed.Graphical abstractHighlights► Phosphorus modified HMCM-22 characterized by multinuclear MAS NMR. ► Reduction of Brønsted acid sites in HMCM-22 by phosphorus impregnation. ► Enhanced selectivity to propylene in MTH reaction over HMCM-22 by phosphorus modification.

Nitrogen-containing MgO-MCM-41 solid base material is prepared by nitridation of MgO-loaded mesoporous MCM-41. The ordered mesoporous structure and high surface area of MCM-41 are well preserved after MgO impregnation and nitridation, as proved by the XRD, TEM and nitrogen adsorption/desorption analysis. FTIR spectra the bridging –NH– groups and terminal –NH2 groups are incorporated into the framework of MgO-MCM-41 by nitridation, and the base strength is expected to be enhanced due to the replacement of oxygen by nitrogen with lower electronegativity. FTIR spectra with the adsorption of different probe molecules, e.g. CO, CD3CN and 13CO2, are employed for the characterization of surface acidic–basic properties of MgO-MCM-41 before and after nitridation. It is revealed that the acidic hydroxyls in MgO-MCM-41 are greatly reduced through nitridation process. Compared with MgO-MCM-41, the nitridized MgO-MCM-41 material exhibits improved basic catalytic performances in Knoevenagel condensation reaction, Claisen–Schmidt reaction and dehydrogenation reaction of 2-propanol.Graphical abstractHighlights► Promising solid base catalyst MgO-MCM-41-N prepared by nitridation of MgO-loaded MCM-41. ► The acidic hydroxyls in parent MgO-MCM-41 greatly reduced through nitridation. ► MgO-MCM-41-N with enhanced basic catalytic properties.

SAPO-34 catalysts obtained after MTO conversion times of 0–30 min were investigated by PFG NMR spectroscopy for studying the self-diffusivities of ethane and ethene. Furthermore, the catalysts were investigated by in situ UV/vis, 13C MAS NMR, and 1H MAS NMR spectroscopy, giving insights into the organic deposits and acid sites in different periods of the catalyst lifetime. The ratio of the self-diffusivities of ethene and ethane, Dethene/Dethane, used as a measure of the diffusion selectivity, was found to increase to the benefit of the olefin compared to the alkane for higher adsorbate loadings and increasing MTO conversion times. This change of the diffusion selectivity is one of the reasons for the variation of the product selectivity during the catalyst lifetime. Variable-temperature PFG NMR studies gave a significantly larger apparent activation energy for the self-diffusivity of ethane (Ea = 7.6 kJ/mol) compared with ethene (Ea = 4.2 kJ/mol).

Heterogeneous photocatalysis offers a promising route to realize green oxidation processes in organic synthesis. In this research, the solvent-free selective photocatalytic oxidation of benzyl alcohol to benzaldehyde in the presence molecular oxygen was studied by using TiO2 and modified TiO2 as photocatalysts. The surface modification of TiO2 by transition metal clusters dramatically enhanced the photocatalytic oxidation activity. Ir/TiO2 prepared by photodeposition showed a remarkably high activity for the photocatalytic oxidation of benzyl alcohol, and an average reaction rate of 14538 μmol h−1 gcat−1 could be obtained. The effect of preparation method, iridium loading and reaction conditions on the catalytic performance of Ir/TiO2 is investigated in detail. Based on the catalytic and characterization results, the problem of product selectivity and the reaction mechanism of the photocatalytic oxidation of benzyl alcohol over Ir/TiO2 are discussed.

Silicoaluminophosphates (SAPO) with different framework structures and amounts of Brønsted acid sites, that is, SAPO-34, SAPO-41, SAPO-11, and SAPO-46, were synthesized and studied as catalysts for the methanol-to-olefin (MTO) conversion. Besides the well-known SAPO-34 catalyst, also SAPO-41 exhibits a good MTO performance with a methanol conversion of 100% and a selectivity to light olefins of about 70% at the reaction temperature of 723 K, which maintains up to a time-on-stream of 10 h. The Brønsted acid sites of silicoaluminophosphate catalysts employed in this study were characterized by means of 1H MAS NMR spectroscopy. These studies were performed with unloaded samples for studying the type and number of OH groups and after loading of ammonia for determining the amount of accessible Brønsted acid sites. The occluded organic species formed on the catalysts during the MTO reaction were analyzed by in situ UV/vis spectroscopy, thermogravimetry-differential thermal analysis (TG-DTA), and gas chromatography-mass spectrometry (GC-MS). On the basis of the characterization and catalytic results, we discuss the effects of Brønsted acid sites and framework structures on the catalytic performance of silicoaluminophosphates in the MTO conversion. The amount of Brønsted acid sites strongly affects the adsorption of methanol and the formation of hydrocarbon pool compounds as well as the catalyst deactivation. On the other hand, the framework structures of the silicoaluminophosphates under study influence the diffusion of products and thus control the product selectivity of the MTO reaction.Keywords: Brønsted acid sites; framework structure; hydrocarbon pool compounds; MTO; silicoaluminophosphate

A series of Me/TiO2 samples (Me = V, Cr, Mn, Fe, Co, Ni, Cu and Zn) with designed Me:TiO2 ratio of 1:10 were prepared by a photodeposition method and studied for the oxidation of CO. The Cu/TiO2 catalyst exhibited remarkably high activity and an overall CO oxidation could be achieved at <100 °C. The effects of activation temperatures, GHSV and initial CO concentration on CO oxidation over Cu/TiO2 were further investigated. XRD, TEM, XPS-AES, H2-TPR and FTIR of CO adsorption were employed to characterize Cu/TiO2 samples and the exact composition of Cu/TiO2 prepared by photo-deposition was determined to be Cu–Cu2O/TiO2. Based on the catalytic and characterization results, the possible mechanism for CO oxidation over Cu–Cu2O/TiO2 was discussed. Finally, the durability and deactivation of Cu–Cu2O/TiO2 during CO oxidation was investigated in time-on-stream reaction.

•High yield of propene in the ETP process obtained on H-SSZ-13.•Improved lifetime in the ETP reaction achieved on dealuminated H-SSZ-13.•Polyalkylnaphthalenes as key active organic species during ETP.•Accumulation of large polycyclic aromatics leads the deactivation of H-SSZ-13.Several types of microporous molecular sieves with similar nSi/nAl ratios (except for SAPO-34) and different pore structures were prepared and applied as ethene-to-propene (ETP) catalysts. H-SSZ-13 zeolite consisting of chabazite cages connected via 8-ring windows possessed the highest adsorption capacity for ethene and exhibited the best activity in the ETP conversion. The decreasing amount of Brønsted acid sites after dealumination of H-SSZ-13 caused a prolonged lifetime of the catalyst in the ETP reaction. The reaction mechanism and deactivation behavior of H-SSZ-13 catalysts during the ETP process were investigated by in situ FT-IR, UV/Vis, GC–MS, TGA and 1H MAS NMR methods. Ethene was rapidly oligomerized and converted into naphthalene-based carbenium ions, playing a significant role in the ETP reaction. The accumulation of these species lead to the formation of polycyclic aromatics, which are responsible for a total blocking of H-SSZ-13 pores, and cause the deactivation of the catalyst.Graphical abstractDownload high-res image (269KB)Download full-size image

Low-silica AlPO-18, AlPO-34, and AlPO-41 with Brønsted site densities of 0.006 to 0.014 mmol/g have been applied as methanol-to-olefin (MTO) conversion catalysts. At 673 K, AlPO-18 and AlPO-34 are active, while AlPO-41 did not exhibit obvious MTO activity. In situ UV/Vis spectroscopy of working AlPO-18 and AlPO-34 shows bands of aromatic compounds, but no formation of these species was found for AlPO-41 with one-dimensional 10-ring pores. This study indicates that the MTO reaction over aluminophosphates requires a minimum Brønsted site density and a suitable framework topology with cages like in AlPO-18 and AlPO-34 allowing the formation and stabilization of aromatics.Download full-size image

Bimetallic Pd–Cu/TiO2 is prepared by successive photo-deposition process and characterized by means of TEM, H2-TPR and FTIR spectra of CO adsorption. The as-prepared Pd–Cu/TiO2 is studied as promising catalyst for nitrate hydrogenation and a step-wise reaction process, divided into nitrate hydrogenation to nitrite and nitrite hydrogenation to nitrogen, is observed. The active sites for nitrate and nitrite hydrogenation over Pd–Cu/TiO2 are discussed individually. It is observed that basic conditions of reaction solution favor the hydrogenation of nitrate to nitrite, while acidic conditions favor the hydrogenation of nitrite to nitrogen. For nitrite hydrogenation, acetic acid is more efficient acidic buffer than hydrochloric acid due to an in situ buffering effect. Based on these results, a two-step process, by changing the reaction solution from basic conditions to acidic conditions at midterm, is developed to realize the hydrogenation of nitrate to nitrogen over bimetallic Pd–Cu/TiO2.Graphical abstractDownload high-res image (145KB)Download full-size imageHighlights► Bimetallic Pd–Cu/TiO2, with typical structure of Cu@Pd@TiO2, is prepared by successive photo-deposition. ► A step-wise reaction process, including nitrate hydrogenation to nitrite and nitrite hydrogenation to nitrogen, is observed. ► A two-step process, by changing the reaction solution from basic conditions to acid conditions at midterm, is developed for nitrate hydrogenation to nitrogen.

Low-silica AlPO-34 materials with similar crystal sizes but different Brønsted acid site densities were prepared and investigated as catalysts in methanol-to-olefin (MTO) conversion. The effect of Brønsted acid site density on catalyst activity and the dominant reaction mechanism during the MTO conversion was investigated via TGA, GC-MS, solid-state NMR spectroscopy, and in situ UV/vis spectroscopy together with the catalytic performance. For the catalysts with lower Brønsted acid site densities, the olefin-based cycle mechanism is the dominant mechanism during the MTO conversion. Long-chain alkenes, e.g., C5–C6 alkenes, act as intermediates that are cracked to lower olefins, or are converted to dienes via hydride transfer reactions, and can also diffuse out of the cages of low-silica AlPO-34 catalysts as the products. With decreasing Brønsted acid site density or reaction temperature, the methylation route of the olefin-based cycle was found to be much more favored than the cracking route. Therefore, a higher selectivity to C5–C6 alkenes (∼50%) is achieved. Simultaneously, dienes are the predominant deposits occluded in the used catalysts. For catalysts with slightly higher Brønsted acid site densities, the long-chain alkenes are rapidly transformed to aromatics and, subsequently, an aromatic-based cycle mechanism contributes to the MTO conversion. Interestingly, the catalyst with the most suitable Brønsted acid site density can well balance the above-mentioned two reaction cycles accompanied by a low deactivation rate, leading to a long catalyst lifetime of up to 15 h.

Fe–MFI prepared by reductive solution ion-exchange was investigated as catalyst for the oxidative dehydrogenation of propane with nitrous oxide, and a maximal propylene yield of ca. 14% could be obtained at the reaction temperature of 673 K. Accumulative acid post-treatments were performed on Fe–MFI and a gradual increase of maximal propylene yield to ca. 25% could be observed. The Fe–MFI samples before and after acid post-treatments were characterized by means of ICP, XRD, DRIFT, TEM, UV-Vis, H2-TPR, NH3-TPD and EPR. The results clearly indicated the transformation of iron species during acid post-treatments. The active iron species in Fe–MFI before and after acid post-treatments were characterized by FTIR spectra of NO adsorption. Based on the characterization and catalytic results, the extra-framework Fe–O–Al species and/or isolated iron species in Fe–MFI were proposed to be more active than oligonuclear iron species for propane dehydrogenation with nitrous oxide.

A one-step hydrothermal route is developed to prepare amino-grafted graphene oxide as an environmentally benign heterogeneous solid base catalyst.

A direct hydrothermal synthesis approach to Fe/ZSM-5 zeolites was developed by using a ferric complex, i.e. ethylenediaminetetraacetic acid ferric sodium (EDTA-FeNa), as both an iron source and a structure-directing agent. During the hydrothermal synthesis, EDTA-FeNa complexes were encapsulated within zeolite channels of ZSM-5 and they underwent transformation to highly dispersed extraframework iron species, i.e. isolated ferric ions and oligomeric FexOy clusters, upon calcination removal of organic species. The as-prepared Fe/ZSM-5 zeolites could be established as bi-functional catalysts containing both acid sites and iron sites. As expected, the as-prepared Fe/ZSM-5 zeolites exhibited remarkable catalytic activity in the selective reduction of nitrogen oxides by ammonia (NH3-SCR), with a nitrogen oxide conversion of >99% in a wide temperature range of 573–693 K under simulated industrial conditions. Meanwhile, good stability and tolerance to water vapor and sulfur dioxide could be achieved, making these Fe/ZSM-5 zeolites promising candidates for practical application. In contrast to conventional post-synthesis modification approaches to Fe/ZSM-5, the one-pot hydrothermal synthesis approach appeared to be very simple and easily reproducible, and the formation of inactive iron oxide nanoparticles can be completely avoided, which accordingly leads to high NH3-SCR activity.

Al-free Fe-beta was prepared from commercial H-beta via a post-synthesis solid-state metallation route and applied as a promising catalyst for selective catalytic reduction of nitric oxide by ammonia. NH3-TPD and FTIR spectroscopy of pyridine adsorption analysis results clearly verify the absence of Brønsted acid sites and the formation of strong Lewis acid sites in the as-prepared Fe-beta zeolite. Isolated ferric ions within a zeolite framework are determined to be the dominating iron species in Fe-beta according to the characterization results from TEM, H2-TPR and UV-vis spectroscopy, and these Fe species are exposed and available for reaction as indicated by FTIR spectroscopy of NO adsorption. Fe-beta exhibited good catalytic activity in NH3-SCR reaction at >573 K, comparable with reference Fe–H-beta prepared via a solid-state ion exchange route, in the presence of SO2 and excess H2O. More importantly, Fe-beta exhibited distinctly better durability in NH3-SCR than reference Fe–H-beta, and a nitrogen oxide conversion of >90% at a reaction temperature of 673 K could be maintained for over 400 h. The remarkable durability of Fe-beta is due to the absence of framework aluminum species and the stabilization of active iron species by the zeolite framework. The reaction mechanism of NH3-SCR over an Fe-beta model catalyst with well-defined active iron sites was finally investigated by means of in situ DRIFT spectroscopy.

The sole effect of surface/bulk defects of TiO2 samples on their photocatalytic activity was investigated. Nano-sized anatase and rutile TiO2 were prepared by hydrothermal method and their surface/bulk defects were adjusted simply by calcination at different temperatures, i.e. 400–700 °C. High temperature calcinations induced the growth of crystalline sizes and a decrease in the surface areas, while the crystalline phase and the exposed facets were kept unchanged during calcination, as indicated by the characterization results from XRD, Raman, nitrogen adsorption–desorption, TEM and UV-Vis spectra. The existence of surface/bulk defects in calcined TiO2 samples was confirmed by photoluminescence and XPS spectra, and the surface/bulk defect ratio was quantitatively analyzed according to positron annihilation results. The photocatalytic activity of calcined TiO2 samples was evaluated in the photocatalytic reforming of methanol and the photocatalytic oxidation of α-phenethyl alcohol. Based on the characterization and catalytic results, a direct correlation between the surface specific photocatalytic activity and the surface/bulk defect density ratio could be drawn for both anatase TiO2 and rutile TiO2. The surface defects of TiO2, i.e. oxygen vacancy clusters, could promote the separation of electron–hole pairs under irradiation, and therefore, enhance the activity during photocatalytic reaction.

A facile fast hydrolysis route to a three-dimensional flow-like iron doped rutile TiO2 nanostructure is developed. With iron species doping into both the bulk phase and the surface, the bandgap narrowing of rutile TiO2 is realized and the dissociative adsorption of water on the surface is promoted, which accordingly lead to greatly enhanced activity in visible-light-driven water oxidation.

Under UV-visible light irradiation, multiple synergetic promotion effects on the photocatalytic activity of TiO2 by gold deposition can be observed, and plasmonic Au/TiO2 shows great potential for photocatalytic solar conversion.

With ethanol as a probe molecule, the surface sites of anatase and rutile can be distinguished using 13C CP/MAS NMR spectroscopy, which offers an opportunity to investigate the transfer of photo-induced electrons from rutile to anatase in the mixed-phase TiO2.

In the present work, the mechanism of the methanol-to-hydrocarbon (MTH) conversion over the silicoaluminophosphate SAPO-41 with one-dimensional 10-ring pores has been investigated. For this purpose, catalytic experiments with co-feeding of reactants, in situ FTIR and UV/Vis spectroscopy, and 1H MAS NMR spectroscopy of used catalysts upon loading of ammonia were performed. Using these methods, only a low content of aromatics could be observed on the working SAPO-41 catalyst. These findings and the characteristic changes in the ethene selectivity during the co-feeding experiments indicate that alkylaromatics can be excluded as active hydrocarbon pool compounds on SAPO-41 applied as MTH catalysts. On the other hand, dienes and enylic carbenium ions were detected using FTIR and UV/Vis spectroscopy and the formation of amines by reaction of alkenes with ammonia was detected via1H MAS NMR spectroscopy. These results are experimental evidence that large olefins partially existing in their carbenium state dominate the catalytically active hydrocarbon pool on the working SAPO-41. Due to this dominant alkene-based reaction mechanism and the limited formation of aromatics, SAPO-41 is a suitable catalyst for the C3+C4 olefin as well as gasoline production.

A series of Me/TiO2 samples (Me = V, Cr, Mn, Fe, Co, Ni, Cu and Zn) with designed Me:TiO2 ratio of 1:10 were prepared by a photodeposition method and studied for the oxidation of CO. The Cu/TiO2 catalyst exhibited remarkably high activity and an overall CO oxidation could be achieved at <100 °C. The effects of activation temperatures, GHSV and initial CO concentration on CO oxidation over Cu/TiO2 were further investigated. XRD, TEM, XPS-AES, H2-TPR and FTIR of CO adsorption were employed to characterize Cu/TiO2 samples and the exact composition of Cu/TiO2 prepared by photo-deposition was determined to be Cu–Cu2O/TiO2. Based on the catalytic and characterization results, the possible mechanism for CO oxidation over Cu–Cu2O/TiO2 was discussed. Finally, the durability and deactivation of Cu–Cu2O/TiO2 during CO oxidation was investigated in time-on-stream reaction.