A facile route was developed to one-step synthesize ZSM-5 hollow microspheres. It was found that their crystallization occurred at near neutral pH with the assistance of EDTA2− ions via a “crystallization in a confined space” mechanism, and the resultant sample gave an exceptional yield of aromatics with a long catalytic lifetime in the methanol-to-aromatics process.

•Ordered mesoporous NbxW(8 − x) oxides were successfully synthesized.•The ratio of Brønsted and Lewis acidic sites was tunable in NbxW(8 − x) oxides.•Nb4W4 is the most active catalyst with 90.2 kJ/mol apparent activation energy.•Reaction network of glucose conversion was established.•Mesoporous Nb4W4 was stable upon four reaction cycles in aqueous solution.A series of ordered mesoporous NbxW(8 − x) oxides with tunable Nb/W ratio were successfully synthesized by evaporation-induced self-assembly method. The mesoporous structure, morphologies, surface chemical state, and acidic properties of these catalysts were fully characterized by low-temperature sorption of N2, small-angle and wide-angle XRD, TEM, Raman, XPS, and Py-IR. It was shown that the NbxW(8 − x) oxides created large amounts of Lewis as well as Brønsted acid sites, which promoted the isomerization of glucose to fructose followed its dehydration to 5-hydroxymethylfurfural (HMF). Mannose was also formed via the epimerization of glucose. Of them, the mesoporous Nb4W4 exhibited the best catalytic activity with a comparatively low Ea about 90.2 kJ/mol and good stability in aqueous medium. The kinetic behavior revealed that Lewis acid sites facilitated to glucose-to-fructose isomerization while Brønsted acid sites promoted the dehydration of fructose to form HMF.Download high-res image (135KB)Download full-size image

A series of ZSM-11 zeolites was synthesized by adding different amounts of boron to a synthesis gel for the purpose of improving its catalytic performance for conversion of methanol to olefins (MTO). It was found that boron has marginal effects on the crystal structure, texture properties and acid site strength of ZSM-11, but it significantly increases its catalytic stability and hydride transfer activity that results in an increase in the amounts of aromatics and alkanes in products. DFT calculations revealed that aluminum and boron atoms competitively enter the ZSM-11 framework. In combination with 27Al MAS NMR, GC-MS, m-xylene isomerization and Co2+-exchanged ZSM-11 diffuse reflectance UV-vis spectroscopy results, it can be deduced that incorporation of boron compels some aluminum atoms to shift towards the intersection T sites, which can greatly alleviate the coking process although it allows the formation of more bulky molecules. This shows that the MTO catalytic performance of ZSM-11 can be largely adjusted by changing the amount of incorporated boron through regulation of aluminum or acid site locations in the framework.

•An unprecedented aromatic yield via direct syngas conversion is obtained•The aromatic selectivity is dependent on the acidity and porous structure of HZSM-5•The pivotal role of the density and strength of acid sites is discussedThe depletion of petroleum reserves threatens economic development and regional stability nowadays. Building an alternative route for fuel and chemical production has become a focused research topic in recent years. Although conversion of syngas to fuels by the Fischer-Tropsch synthesis (FTS) process has been industrialized in various countries, expanding its products to value-added chemicals is still a great challenge. Aromatics are very important feedstock; they are used as blending mixtures for gasoline with a high octane number in some countries and are the most important molecular platform for the polymer industry. With the fast development of the polymer industry, the gap between supply and demand calls for a new strategy for the synthesis of aromatics. We have established an intriguing process that directly converts syngas to aromatics on the basis of a physical mixture of a highly effective FTS catalyst and zeolite, which shows enormous potential in comparison with the traditional multiple-step pathway.Direct synthesis of aromatics from syngas is a great challenge because of severe operating conditions and low yield of aromatics. Making this process more competitive than the MTA (methanol to aromatics) process will require high energy efficiency and low CO2 emission. A combination of Na-Zn-Fe5C2 and hierarchical HZSM-5 with uniform mesopores dramatically changed the product distribution of Fischer-Tropsch synthesis, leading to 51% aromatic selectivity under the stable stage with CO conversion >85%. C12+ heavy hydrocarbons almost disappeared, and the catalyst showed good stability. The hierarchical zeolitic structure and Brønsted acidity of HZSM-5 could be precisely tuned by controlling the alkali treatment conditions and the degree of ion exchange. The appropriate density and strength of the Brønsted acid sites and the hierarchical pore structure of HZSM-5 endowed the catalyst with an unprecedented aromatic yield. This work shows a broad area for development for syngas conversion.Download high-res image (213KB)Download full-size image

•Modified graphene oxide (abGO) was synthesized by successive base and acid treatment.•The abGO has been demonstrated as an advanced metal-free carbon catalyst.•The abGO gave superior performance for oxidation of benzyl alcohol to benzaldehyde.•The abGO presented excellent stability and substrate adaptability.•Surface phenol hydroxyl groups are the intrinsic active sites.The graphene-based materials, particularly graphene oxide (GO) with rich oxygenated groups, exhibit high catalytic performance in various metal-free oxidation reactions. However, the intrinsic active site is still unclear, which greatly retards to further develop advanced catalysts. Here, the modified graphene oxide (abGO) was synthesized by sequential base and acid treatment and employed in the aerobic oxidation of benzyl alcohol to benzaldehyde. This novel catalyst displayed much higher activity, selectivity and stability than that of conventional GO. 93.1% conversion and 100% selectivity were achieved over abGO. More importantly, it is shown that the yield of benzaldehyde is linearly proportional to the content of surface phenol hydroxyl groups. Experimentally observed reactivity trends, structure-behavior correlation, molecule mimicking and characterization results strongly confirm that the surface phenol hydroxyl groups are the intrinsic active sites.Download high-res image (134KB)Download full-size image

One-pot hydrogenolysis of cellulose to ethylene glycol (EG) was carried out on WO3-based catalysts combined with Ru/C. To probe the active catalytic site for breaking the C–C bond of cellulose, a series of WO3–ZrO2 (WZr) catalysts were synthesized and systematically characterized with XRD, Raman, UV-Vis, H2-TPR, DRIFS and XPS techniques and N2 physisorption experiment. It was found that the WO3 crystallites became more easily reduced to W5+–OH species with increasing crystallite size or tungsten surface density of the WZr catalyst owing to the decrease of their absorption edge energy (AEE) originating from weakening their interaction with ZrO2 support. This, as a result, gave higher EG yield at higher tungsten surface density. The structure–activity relationship of the WZr catalyst reveals that the active catalytic site for cleaving the C2–C3 bond of the glucose molecule is the W5+–OH species.

•Pilot scale reverse flow reactor demonstrated for ventilation air methane mitigation•A kind of non-noble metal catalyst was used and tested in the reverse flow reactor.•Hot gas withdrawal was used to recover part of heat from methane oxidation.•Reactor control and heat recovery schemes proposed previously were verified.•Switch time affects heat recovery efficiency; hot gas removed impacts reactor stability.The mitigation and utilization of ventilation air methane was demonstrated in a pilot scale catalytic reverse flow reactor. A kind of non-noble metal oxide catalyst of 1.8 m3 was loaded and lean methane with a concentration of 0.2–1.0 vol% and a maximum feed flow rate of 800 m3/h was processed. The schemes of reactor control and heat recovery, viz., a simple logic-based controller plus hot gas withdrawal from reactor center, as proposed previously by simulation, were verified in this pilot scale reactor. The results prove that the autoregulative time to switch the gas flow direction will drop quickly to zero if a large amount of hot gas is withdrawn from the reactor by using the traditional method. The switching time has a great influence on the heat recovery efficiency, whereas the amount of hot gas removed out of the reactor impacts significantly on the reactor stability. All these experimental observations are in line with the simulation results. The long term operation proves the feasibility of hot gas withdrawal with a heat recovery efficiency of about 56% and the reliable performances of the non-noble metal catalyst in lean methane oxidation with a methane conversion over 90%. These results prove that the catalytic reverse flow reactor and control schemes used in this work are quite effective in the mitigation and utilization of lean methane.A pilot scale catalytic reverse flow reactor was demonstrated for the mitigation and utilization ventilation air methane; the schemes of reactor control and heat recovery proposed previously by simulation were verified.Download high-res image (300KB)Download full-size image

The high-yield synthesis of the biofuel γ-valerolactone (GVL) is a challenging task, which currently stems from the depolymerization of cellulose to levulinic acid, followed by its hydrogenation. We have developed a novel integrated process for the production of GVL from hemicellulose without using liquid acids and external hydrogen. The hemicellulose feed underwent hydrolysis and consecutive dehydration to produce furfural over ZSM-5 catalyst. Subsequently, the formed furfural with 2-propanol performed tandem conversion to GVL over Au/ZrO2 catalyst combined with ZSM-5. This process gave a high yield of GVL under mild conditions: up to 61.5% based on hemicellulose. The outstanding performance was mainly ascribed to the strong interface interaction of Au with ZrO2 species, large amounts of medium-strength acid sites over ZSM-5, and efficient synergy between active metal and acid sites.Keywords: Au; furfural; hemicellulose; ZSM-5; γ-valerolactone

A series of sustainable porous carbon materials were prepared from waste polyurethane foam and investigated for capture of CO2. The effects of preparation conditions, such as precarbonization, KOH to carbon precursor weight ratio, and activation temperature, on the porous structure and CO2 adsorption properties were studied for the purpose of controlling pore sizes and nitrogen content and developing high-performance materials for capture of CO2. The sample prepared at optimum conditions shows CO2 adsorption capacities of 6.67 and 4.33 mmol·g–1 at 0 and 25 °C under 1 bar, respectively, which are comparable to those of the best reported porous carbons prepared from waste materials. The HCl treatment experiment reveals that about 80% of CO2 adsorption capacity arises from physical adsorption, while the other 20% is due to the chemical adsorption originated from the interaction of basic N groups and CO2 molecules. The relationship between CO2 uptake and pore size at different temperatures indicates that the micropores with pore size smaller than 0.86 and 0.70 nm play a dominant role in the CO2 adsorption at 0 and 25 °C, respectively. It was found that the obtained carbon materials exhibited high recyclability and high selectivity to adsorption of CO2 from the CO2 and N2 mixture.

A new type of interconnected hollow graphitic vesicle (HGV-T) with high purity was successfully synthesized by pyrolysis of cyclohexane over Co3O4 nanoparticles. Heat treatment was proven to be an effective way to make the shell permeable, thus allowing to easily remove metal core by facile acid leaching at room temperature. The overall transition process was investigated in detail on the basis of the structures of formed carbons and the crystal changes of cobalt species at different reaction stages. It was found that the wall thickness of HGV-T could be tailored by varying the deposition time, and the graphitization degree of HGV-T was highly dependent on the annealing temperature. Upon support of Pt, HGV-T shows much higher electrocatalytic activity and durability than commercial Pt/C catalyst in the oxygen reduction reaction as results of its open hollow network, high dispersion of Pt, excellent electrical conductivity and high corrosion resistance. The electrocatalytic activity of Pt/HGV-700 is 2.7 times as high as that of commercial Pt/C under the same testing conditions, which endows it with a potential for serving as an alternative support of fuel cell.

A series of SBA-15-supported WO3 catalysts was prepared by impregnating silicotungstic acid on SBA-15 (HSiW-SBA-15) and subsequently calcining at different temperatures. It shows higher catalytic activity and stability than the physical mixtures of SBA-15 and WO3 in the self-metathesis of 1-butene to propene. The calcination temperature of HSiW-SBA-15 has a significant effect on its catalytic performance. The sample calcined at 700 °C gave a 1-butene conversion and a propene selectivity of 59.6% and 59.7%, respectively, at 350 °C. It was found that the metathesis of 1-butene to propene occurred via two steps. The first one was isomerization of 1-butene to 2-butene on both Brønsted and Lewis acid sites, and the second one was metathesis of 1-butene and 2-butene to propene via the formation of W-carbene species (WCHCH3, WCH2 and WCHCH2CH3). The Si–O–W–OH Brønsted acid sites play a decisive role in the formation of W-carbene species, and the pseudo-Wittig mechanism dominates the process.

On the basis of density functional theory including dispersion correction (ωB97XD), the thermodynamics and kinetics of the formation of polymethylbenzene intermediates in methanol to olefin conversion over zeolites with different pore sizes have been systematically computed. The agreement between the experimental and theoretical adsorption enthalpies of the several polymethylbenzenes over H-FAU reasonably validates the applied models and methods, and reveals the importance of dispersion correction in the space confinement and electrostatic stabilization of the zeolite framework. The free energies of the stepwise formation of the polymethylbenzenes show that the most favorable active hydrocarbon pool intermediates are pentamethylbenzene and hexamethylbenzene over H-BEA and H-SAPO-34, as well as tetramethylbenzene over H-ZSM-5 and H-ZSM-22. These stable polymethylbenzenes are also precursors for the formation of geminal methylated cationic intermediates on the basis of kinetic and thermodynamic analyses. The agreement of the thermodynamic and kinetic results on the favorable intermediates validates the use of Gibbs free reaction energies to estimate the primary component of the intermediates in the various zeolites. All these pore-size-dependent differences among the zeolites show their enhanced confinement effect, which is mainly influenced by the short-range electrostatic potential including stabilization and repulsion.

A clear understanding of the methane formation mechanism in the initial MTO process is beneficial for the illustration of the initial C–H bond activation mechanism and the first C–C bond formation route. Thus, attempts are made here to unravel the methane formation pathway in the initial MTO process by elaborately designing experiments. It is shown that methane is generated together with formaldehyde or methoxymethyl cation by attacking the C–H bond of methanol or dimethyl ether (DME) with surface methoxy species (SMS). The reaction of DME and SMS provides strong evidence for the occurrence of C–H bond cleavage and the “methoxymethyl cation mechanism” in the initial MTO process.

•The catalytic properties of H-[Al,B]-MWW for methylation of ethene were studied.•Effects of dealumination by various acids on catalytic properties were discussed.•Catalytic properties can be greatly improved by dealuminating with oxalic acid.•Types, strength and locations of acid sites greatly affect catalytic properties.Hydrothermally synthesized H-[Al,B]-MWW zeolite was dealuminated with oxalic, nitric and citric acids. The obtained samples were characterized with XRD, ICP-AES, FT-IR, NH3-TPD, pyridine-adsorption IR, 27Al MAS NMR techniques and nitrogen sorption experiment. Citric acid mainly removed the acid sites located on the external surface pockets with small amounts of extraframework Al species retained in the interlayer void space, while nitric acid leached both the internal (sinusoidal channels and supercages) and the external surface (side pockets) acid sites although significant amounts of extraframework Al species were generated in the sinusoidal channels. As for the oxalic acid, it primarily eliminated the acid sites in the supercages and side pockets without generation of considerable amounts of extraframework Al species in the internal channels, consequently greatly increasing the catalytic stability of the sample in methylation of ethene by methanol. The sample dealuminated with oxalic acid for 24 h showed a catalytic life of 300 h as a result of a reduction in coking rate.

A versatile SnO2@graphene nanocomposite with a mesoporous structure was prepared by a facile and green solvothermal method. The nanocomposite exhibited high response to low-concentration HCHO (1 ppm) at low working temperature (120 °C). The response and recovery times are 1 s and 85 s for 1 ppm formaldehyde. There is an excellent linear relationship (R = 99.798%) between response and the concentration of HCHO in a large range (1–100 ppm).

On the basis of density functional theory including dispersion correction [ωB97XD/6-311+G(2df,2p)//B3LYP/6-311G(d,p)], the thermodynamics and kinetics of the reactions of CH3OH and CH3OCH3 over H-ZSM-5 have been systematically computed. For the reaction of the methylated surface (CH3OZ) with CH3OH, CH3OCH3 formation is kinetically controlled and the competitive formation of CH2O + CH4 is thermodynamically controlled, in agreement with the observed desorption temperatures of CH3OH, CH3OCH3, and CH2O under experimental conditions. For the reaction between ZOCH3 and CH3OCH3, the formation of the framework stabilized (CH3)3O+ is kinetically controlled, consistent with the NMR observation at low temperature, and the competitive formation of surface CH3OCH2OZ + CH4 is thermodynamically controlled. On the basis of the thermodynamically more favored CH2O and CH3OCH2OZ, there are two parallel routes for the first C–C bond formation, from the coupling of CH3OCH2OZ with CH3OH and CH3OCH3 as well as from the coupling of CH2O with CH3OH and CH3OCH3. The most important species is the methylated surface (CH3OZ), which can react with CH3OH and CH3OCH3 to form the corresponding physisorbed CH2═O and chemisorbed CH3OCH2OZ, and they can further couple with additional CH3OH and CH3OCH3 to result in first C–C formation, verifying the proposed formaldehyde (CH2O) and methoxymethyl (CH3OCH2OZ) mechanisms.

The methanol to hydrocarbon (MTH) process provides an efficient route for the conversion of carbon-based feedstocks into olefins, aromatics and gasoline. Still, there is room for improvements in product selectivity and catalytic stability. This task calls for a fundamental understanding of the formation, catalytic mechanism and degradation of active sites. The autocatalytic feature of the MTH process implies that hydrocarbons are active species on the one hand and deactivating species on the other hand. The steady-state performance of such species has been thoroughly studied and reviewed. However, the mechanism of formation of the initial hydrocarbon species (i.e.; the first C–C bond) and the evolution of active species into deactivating coke species have received less attention. Therefore, this review focuses on the significant progress recently achieved in these two stages by a combination of theoretical calculations, model studies, operando spectroscopy and catalytic tests.

Graphene and its derivatives (graphene oxide and reduced graphene oxide) have attracted a great deal of attention and have been widely applied in the field of catalysis science owing to their exceptional physical properties and chemical tunability. This review focuses on the advances of graphene-based materials in catalytic transformation of biomass and platform molecules to value-added chemicals and biofuels, with emphasis on the development of these materials directly as catalysts and promising supports to anchor Brønsted acid sites in addition to metal nanoparticles. The state-of-the-art and future challenges of graphene-based catalysts in biomass utilization are also discussed.

The catalytic properties of H-MCM-22 zeolites with Si/Al ratios in the range from 13.5 to 47 and their dealuminated samples were investigated in the conversion of methanol to hydrocarbons. The fresh and spent samples were characterized with XRD, NH3-TPD, pyridine-adsorption infrared spectroscopy, 27Al MAS NMR spectroscopy, TG-DTA, GC-MS, diffuse reflectance UV-vis, Raman spectroscopy techniques and nitrogen and p-xylene adsorption experiments. Although a decrease in protonic acid sites, as expected, increased the selectivity to light olefins such as propene and butene, the sample with a Si/Al ratio of 25–37 showed higher catalytic stability. It is worth noting that the external surface acid sites have a pronounced effect on the catalytic performance. Selective removal of these acid sites by dealumination with oxalic acid markedly increased the catalytic stability. This is because the acid sites in the supercages and external side pockets quickly induced formation of deposited coke species, which blocked the sinusoidal channels and caused the deactivation of the catalyst.

Effects of pore structures of ZSM-5, MOR, Beta and USY on their catalytic properties in the transalkylation of toluene with 1,2,4-trimethylbenzene (1,2,4-TMB) were investigated by studying the catalytic mechanism and the diffusion behavior of reactants and products. The medium-pore ZSM-5 shows low catalytic activity as a result of slow decomposition of diphenylmethane (DPM) intermediates and occurrence of severe cracking of 1,2,4-TMB via the monomolecular reaction pathway. In contrast, the large-pore MOR, Beta and USY zeolites allow rapid formation and transformation of bulky DPM species, consequently exhibiting higher catalytic activity. The diffusion experiments show that 1,2,4-TMB and 1,2,4,5-tetramethylbezene (1,2,4,5-TeMB) more easily diffuse into/out of the pores of MOR zeolite than of Beta and USY. Thus, the disproportionation of 1,2,4-TMB and coking were inhibited in MOR, which makes it exhibit higher catalytic stability and xylene selectivity. A detailed analysis of the deposited coke species with GC-MS indicates that the transalkylation of toluene with 1,2,4-TMB occurs via the bimolecular intermediate mechanism.

A two-dimensional mesoporous carbon nitride (MCN-1) material with tunable surface area, pore volume and nitrogen content has been synthesized by using carbon tetrachloride and ethylenediamine as precursors and SBA-15 as a template. The effect of the carbonization temperature on the textural properties, N content and the types of nitrogen species of the MCN-1 samples was also investigated by several characterization techniques. The results reveal that the higher temperature favors the formation of porous structure during the thermal condensation process. In addition, the nitrogen content and the surface N/C ratio in the samples monotonically decrease with the increase of carbonization temperature. The catalytic activity of MCN-1-T is not only related to its surface nitrogen content but also dependent on the structural diversities of the surface nitrogen species. The MCN-1 sample synthesized at 400 °C shows the higher catalytic activity and stability for Knoevenagel condensations.

A series of renewable nitrogen-containing granular porous carbons with developed porosities and controlled surface chemical properties were prepared from poplar anthers. The preparation conditions such as pre-carbonization and activation temperatures and KOH amount significantly influence the structures and chemical compositions of the porous carbons, the CO2 adsorption capacities of which are highly dependent on their pore structures, surface areas, nitrogen contents and adsorption conditions. The sample with developed microporosity, especially with the pores between 0.43 and 1 nm and high nitrogen content shows high CO2 adsorption capacity at 1 bar and 25 °C. In contrast, when the adsorption pressure is higher than 5 bar, its CO2 adsorption capacity is dominated by its surface area, and more accurately by its pore volume. Irrespective of this, if the pressure was decreased to 0.1 bar, its CO2 capture ability is closely correlated to its nitrogen content but not to its porosity. By optimizing the preparation conditions, a porous carbon with a surface area of 3322 m2 g−1 and a CO2 adsorption capacity as high as 51.3 mmol g−1 at 50 bar and 25 °C was prepared.

•Chloromethylation was performed on phenylene sites in the framework of PMOs.•Amination of PMOs was achieved via reacting –C4H3CH2Cl– with piperazine.•RuSalen could be covalently attached on aminated PMOs.•RuSalen on aminated PMOs showed higher activity in cyclohexene oxidation with H2O2.•RuSalen on aminated PMOs were more stable than that on aminated SBA-15.A new approach was employed to prepare metal complex-functionalized periodic mesoporous silica. This approach mainly involves the following three steps, that is, chloromethylation of –C6H4– sites in the framework of PMOs into active –C6H3CH2Cl–, amination of PMOs via reacting –C6H3CH2Cl– with piperazine and covalent attachment of RuSalen by refluxing the aminated PMOs in RuSalen ethanol solution. The obtained hybrid material was characterized with XRD, N2 sorption, FTIR, diffuse reflectance UV–vis spectroscopy, TEM and 13C MAS NMR techniques. It shows higher activity and stability in the oxidation of cyclohexene with H2O2 than the corresponding RuSalen functionalized SBA-15 prepared by the similar method except that the introduction of active –C3H6Cl was achieved by grafting 3-chloropropyltriethoxysilane on SBA-15.

Nitrogen-containing porous carbon materials are ubiquitous with a wide range of technologically important applications, including separation science, heterogeneous catalyst supports, water purification, electrochemistry, as well as the developing areas of energy generation and storage applications. To date, a variety of approaches has been developed and applied to introduce nitrogen into the carbon matrix. It is important and necessary to design and control a hierarchical porous structure and the surface chemical groups of nitrogen-containing porous carbons for their applications. In this work, we summarize and compare recently reported routes for the preparation of nitrogen-containing porous carbon materials and the effect of nitrogen groups on its applications in adsorption, electrochemistry, catalysis/catalyst supports and hydrogen storage properties.

A novel strategy to synthesize a size-selective catalyst consisting of a Pd-containing silica core and an outer silica shell with controllable pore size, was developed. Such intended structures were confirmed with N2 sorption, XRD, TEM and SEM. The pore sizes on the shell could be further tailored through silylation with organosilanes with variable chain lengths. This intriguing nanostructured catalyst showed a high activity in the aerobic oxidation of alcohols. Impressively, when the pores on the shell were tailored to particular sizes the catalyst exhibited size-selective catalysis, and the substrate molecules with only a slight difference in molecular size could be discriminated. This study potentially supplies a new approach for constructing size-selective catalysts.

Ti-rich Ti-YNU-1 has been successfully prepared by using acid-treated Fe-YNU-1 as silica source. Its Ti/Si molar ratio was increased from 0.0065 maximally achieved by the conventional method (Appl. Catal. A (2011), 401, 37–45) to 0.012. The diffuse reflectance UV–vis spectroscopy reveals that most of Ti species had a tetrahedral coordination. This is further substantiated by the presence of a broad band at 930 cm−1, which is characteristic for the incorporation of Ti in the framework. As a result, the prepared Ti-rich Ti-YNU-1 gave considerably higher conversions of both 1-hexene and cyclohexene than the sample prepared by the conventional method. Nevertheless, the increase degree of 1-hexene conversion was much higher than that of cyclohexene conversion with increasing Ti content, suggesting that most of additional Ti species were incorporated into the intralayer sinusoidal 10-membered ring channels, while a few was inserted into the interlayer supercages. Removal of most of occluded templating molecules and framework Fe species or Ti species from the postsynthesized lamellar Fe- or Ti-MWW precursor by acid treatment is necessary for the formation of Fe- or Ti-YNU-1.Graphical abstractHighlights► Ti-rich Ti-YNU-1 was prepared using highly acid-treated Fe-YNU-1 as silica source. ► Ti-rich YNU-1 shows high activity for the oxidation of both linear and bulky alkenes. ► Removal of most of templating and metal species by acid treatment is necessary for forming YNU-1. ► Postsynthesis conditions of the lamellar precursor influence the formation of YNU-1.

Two methods were used to control the crystal size of ZSM-5 synthesized with commercial silica sol. One is use of organic additives; the other is use of colloidal silicalite-1 seed. Addition of polyethylene glycol (PEG) to the synthesis gel favors the formation of relatively small uniform crystals because of promotion of nucleation and somehow hindering the growth of crystals, although it has little influence on the structure, crystallinity, acidity, and crystal shape. The prepared catalyst shows higher catalytic stability than the sample synthesized with the PEG-free gel in the methanol-to-hydrocarbon (MTH) reaction. Finely controllable synthesis of different-sized ZSM-5 crystals was realized by epitaxially growing ZSM-5 crystals around colloidal silicalite-1 seed. The crystal size could be tuned from 200 to 1000 nm by every 100 nm through adjusting the crystallization time and the amount of the added silicalite-1 seed. This makes it possible to systematically study the effect of zeolite crystal size on its catalytic performance and tune product distribution. A significant increase in the catalytic stability was observed with decreasing crystal size for ZSM-5 catalyzing MTH reaction. The crystals with a size of about 270 nm showed a catalytic life of about 6 and 3 times as long as those of the samples synthesized in the absence and presence of PEG respectively.Graphical abstractHighlights► Addition of PEG to the synthesis gel favors the formation of uniform ZSM-5 crystals. ► Fine tuning of ZSM-5 crystal size was realized by adjusting colloidal silicalite-1 seed amount. ► Catalytic properties of ZSM-5 in methanol-to-hydrocarbon reaction depend on its crystal size. ► A silicalite-1 core-ZSM-5 shell composite with tunable shell thickness were synthesized.

Hierarchical porous activated carbon fibers with a BET surface area of 2231 m2 g−1 and a pore volume of 1.16 cm3 g−1 were made from polyacrylonitrile through pre-oxidation and chemical activation. This type of material contains a large amount of nitrogen-containing groups (N content > 8.1 wt%) and consequently basic sites, resulting in a faster adsorption rate and a higher adsorption capacity for CO2 than pure carbon materials with analogous structures under the same conditions. Moreover, its adsorption capacity for CO2 was more than 3.3-times higher than that for N2. In particular, it showed a much higher CO2 adsorption capacity than zeolite 13X, which is conventionally used to capture CO2, in the presence of H2O.

Density functional theory (DFT) calculations were employed to investigate the positions of Al in the framework of Na-MCM-22 as well as the locations and strengths of Brönsted acid sites in the corresponding H-MCM-22 analogue. Thermodynamically, the most favorable sites for locating Al are T7 and T1 sites, followed by T5, T3 and T4, while T2, T8 and T6 sites are unlikely to be occupied because of less stability. Accordingly, two types of Si(OH)Al groups, viz. isolated and H-bonded bridging OH species, were found in H-MCM-22. This finding is supported by the perfect agreement between the calculated and experimentally observed OH vibrational frequencies. The calibrated N2 and CO adsorption energies on the bridging OH sites reveal stronger Brönsted acidity of Al3–O13H–Si3 and Al4–O7H–Si4 sites than Al1–O3H–Si4 and Al3–O12H–Si3 sites.Graphical abstractResearch highlights► Framework Al distribution in MCM-22 was studied with Na+ as counter-cation. ► The most probable sites for locating Al are T7 and T1, while T2, T8 and T6 are much less stable. ► Both isolated and H-bonded Si–OH–Al species were contained in H-MCM-22. The calculated OH frequencies agree well with the experimentally observed values. ► Al3–O13H–Si3 and Al4–O7H–Si4 show stronger acidity than Al1–O3H–Si4 and Al3–O12H–Si3.

Effects of ammonium salts on the synthesis and characteristics of TS-1 were studied by adding different ammonium salts (NH4F, NH4Cl, NH4Br, NH4I, CH3COONH4, NH4NO3, (NH4)2CO3, (NH4)2SO4 and (NH4)3PO4) to the synthesis gel. It was shown that the fine structure and crystal morphology of the synthesized materials depended on the type of ammonium salts. Except for NH4F, the ammonium salts, and particularly (NH4)2SO4 and (NH4)3PO4 significantly decreased the crystallization rate as a result of remarkably reducing the pH value of the crystallization mixture. Nevertheless, all of these ammonium salts were favorable for the incorporation of Ti in the framework, and the beneficial effect was dependent on the type of ammonium salts. In addition, the ammonium salt also has a strong influence on the catalytic properties of the prepared catalyst. It is worth noting that the catalytic performance of TS-1 was closely related to the substrate molecules. TS-1 catalyst prepared in the presence of (NH4)2SO4 gave the highest conversion in the epoxidation of 1-hexene, whereas that prepared with (NH4)2CO3 was suitable for the oxidation of phenol.

A stable heterogeneous organotin catalyst has been prepared by in situ tethering organotin compounds on SBA-15. This was verified by XRD, TEM, N2 adsorption/desorption at −196 °C, FTIR and diffuse reflectance UV–vis spectral techniques. This material was much more active than the sample prepared by the grafting method for the direct synthesis of dimethyl carbonate (DMC) from methanol and CO2 despite that its catalytic activity was dependent on the organotin amount. This could be attributed to the formation of organotin clusters with different structures and the larger surface area. After immobilization on the SBA-15 mesoporous material, the six-coordinated organotin clusters showed higher activity, compared to the tetrahedral Sn species. With increasing reaction temperature and CO2 pressure, the catalytic activity considerably increased.

Selective oxidation of alcohols to aldehydes/ketones with O2 over a series of supported gold catalysts was studied. The catalytic performance depends strongly on the support. It is also strongly influenced by the preparation method and the pH value and stirring rate during the co-precipitation process as a result of their effect on the structure of the support and the particle size and electronic state of gold. The Au/CuO co-precipitated at pH 10 and stirring rate 100 rpm showed high activity, selectivity, and stability. The reaction might occur via oxidative dehydroxylation of alcohols to aldehydes/ketones by direct β-CH elimination, as indicated by the IR result. The oxidation of different cycloalcohols showed that the activity increased with an increase in their methyl groups. Both conversion and ketone selectivity higher than 99% were achieved for cyclooctanol and cyclododecanol.Graphical abstractSelective oxidation of alcohols with O2 to aldehydes or ketones on supported Au catalyst was studied. The Au/CuO with appropriate-sized gold nanoparticles and cationic gold species shows high activity, selectivity and stability for a range of cyclic, benzylic, and unsaturated alcohols. The reaction probably occurred via an integrated oxidation mechanism.Download high-res image (180KB)Download full-size imageHighlights► Au/CuO shows high activity, selectivity, and stability for the oxidation of alcohols with O2. ► Support structure and catalyst preparation process greatly influence the catalytic properties. ► Introduction of base or use of toluene solvent significantly increases the catalyst stability. ► The reaction occurs via an integrated oxidation mechanism involving lattice oxygen of CuO.

•Framework Al distribution of Al-Ge-ITQ-13 has remarkable effects on its MTP catalytic properties.•Al locations in the Al-Ge-ITQ-13 framework can be regulated by adjusting Ge and Al content in gel.•Locating Al at T3 and T6 sites makes Al-Ge-ITQ-13 show high catalytic stability and propene selectivity.•A method for estimating acid site distribution and density effects on catalytic life was developed.•Al-Ge-ITQ-13 shows very high hydrothermal stability.Locations of Al in the Al-Ge-ITQ-13 framework were regulated by adding different amounts of Ge and Al for the purpose of developing a potential methanol-to-propene catalyst. Ge had no significant influence on acid site number, strength, and type, but influenced acid site distribution and catalytic properties. The Al sited at T2, T5, and particularly T9 sites rapidly deactivated Al-Ge-ITQ-13, but attempts to locate Al at T3 and T6 by adjusting Ge and Al content remarkably increased its catalytic life and propene selectivity, by 686% and 44% respectively. A simple method for roughly estimating the great effects of acid site distribution and density on the catalytic life was developed by measuring the intensity of 27Al MAS NMR signal around 51.4–53.4 ppm, even though changes in acid site density are always accompanied by alterations of acid site distribution. The hydrothermal treatment of Al-Ge-ITQ-13 confirms its potential for use in industry.Download high-res image (110KB)Download full-size image

•g-C3N4 was synthesized by thermal condensation of dicyandiamide and urea.•g-C3N4 exhibits excellent performance in the Knoevenagel condensation reactions.•Four types of N-containing species are present, NH2, NH, N(C)3, and CNC.•The activity of g-C3N4 depends on the amount and structure of surface N species.•The activity of nitrogen species follows the order NH2 > NH > N(C)3 > CNC.Graphitic carbon nitride (g-C3N4) with high nitrogen content and surface area was synthesized by the thermal condensation of dicyandiamide and urea. This method gave a much higher product yield than the direct thermal decomposition of urea. The prepared g-C3N4 is active for the Knoevenagel condensation of an aldehyde or ketone with methylenic compounds, but the activity depends on the structure of basic nitrogen species. Fourier transform infrared and X-ray photoelectron spectroscopy show that at least four types of nitrogen species are present in g-C3N4, including primary amines (NH2), secondary amines (NH), tertiary nitrogen (N(C)3), and pyridinic nitrogen (CNC). The amounts and types of these nitrogen species in g-C3N4 are closely related to the urea/dicyandiamide ratio in its precursor mixture. The catalytic activity of these nitrogen species in the inactivated Knoevenagel condensation system decreases in the order of NH2 > NH > N(C)3 > CNC, while it is similar for the NH2 and NH species in the activated reaction system. This trend provides strong evidence for the abstraction of a proton from the methylenic compounds as the rate-determining step. The prepared g-C3N4 is highly stable and reusable in the Knoevenagel condensation reactions.Download high-res image (84KB)Download full-size image

•The existence of the direct mechanism in initial MTO process was evidenced.•A critical intermediate of CH3OCH2+ was detected and theoretically verified.•A convincing route for formation of original C–C bond in MTO process was proposed.•Propene was found to be the initial olefin product in the MTO process.The formation mechanism of the original C–C bond in methanol conversion to hydrocarbons over zeolite catalysts remains a grand challenge, although many researchers have done a lot of work and made significant progress. Here, a convincing route for formation of initial hydrocarbon pool (HCP) species involving original C–C bonds from dimethyl ether (DME) and/or methanol is illustrated by combining coincident experimental and theoretically calculated results. Elaborate experimental results gave strong evidence for predominant direct mechanism in the initial methanol-to-olefins process catalyzed by SAPO-34. A critical intermediate of the methoxymethyl cation was detected and theoretically verified through the reaction of the methoxy group and DME. This intermediate species subsequently reacted with DME or methanol to produce C–C bond-containing compounds 1,2-dimethoxyethane or 2-methoxyethanol. Further formation of oxonium cations led to generation of ethers or alcohols, and further to propene as the primary alkene product that induced the occurrence of the HCP mechanism.Graphical abstractDownload high-res image (77KB)Download full-size image

H-Al-MWW with different Si/Al ratios has been synthesized in the presence of hexamethyleneimine by the postsynthesis method with the ion-exchange of Na+ with NH4+ unnecessary. However, irrespective of the framework Si/Al ratio, the as-synthesized Al-MWW lamellar precursor was not transformed into the Al-YNU-1 phase by the method used for preparing Ti-YNU-1 [W. Fan, P. Wu, S. Namaba, T. Tatsumi, Angew. Chem. Int. Ed. 43 (2004) 236]. This may be due to the difficulty in removing hardly oxidized hexamethyleneimine molecules by acid treatment, as shown by TG/DTA measurement results. In combination with 13C CP/MAS NMR spectroscopy, it was indicated that these hardly oxidized hexamethyleneimine molecules might strongly interact with the zeolite framework or be tightly constrained between the layers. Nevertheless such a type of templating molecules could be washed away by acid when piperidine was used as a template. As a result, H-Al-YNU-1 with a pore opening intermediate between those of H-Al-MOR and H-Al-Beta was successfully prepared in the way adopted for preparing Ti-YNU-1. This material showed much higher activity than H-USY, H-Al-MOR, H-Al-Beta, H-Al-MWW, H-Al-ZSM-5, and interlayer-expanded H-Al-MWW through silylation in alkylation of anisole with benzyl alcohol and acylation of anisole with acetic anhydride as a result of its enlarged pore opening connected to supercages and predominant moderately strong Brönsted acid sites. The benefit of the large pore opening of H-Al-YNU-1 was also confirmed by the catalytic results obtained in the Baeyer–Villiger reaction of cyclohexanone with bulkiness corresponding to 12 membered-ring pore openings.H-Al-YNU-1 with a 12-MR pore opening and H-Al-MWW with different Si/Al ratios were postsynthesized in the presence of piperidine (PI) and hexamethyleneimine (HMI) with the ion-exchange of Na+ with NH4+ unnecessary. H-Al-YNU-1 was not obtained by acid treating and subsequently calcining the Al-MWW lamellar precursor synthesized with HMI, but it could be prepared in such a way when PI was used, and showed high activity in alkylation of anisole with C6H5CH2OH and acylation of anisole with (CH3CO)2O.Download high-res image (79KB)Download full-size image

Hierarchical porous activated carbon fibers with a BET surface area of 2231 m2 g−1 and a pore volume of 1.16 cm3 g−1 were made from polyacrylonitrile through pre-oxidation and chemical activation. This type of material contains a large amount of nitrogen-containing groups (N content > 8.1 wt%) and consequently basic sites, resulting in a faster adsorption rate and a higher adsorption capacity for CO2 than pure carbon materials with analogous structures under the same conditions. Moreover, its adsorption capacity for CO2 was more than 3.3-times higher than that for N2. In particular, it showed a much higher CO2 adsorption capacity than zeolite 13X, which is conventionally used to capture CO2, in the presence of H2O.

Graphene and its derivatives (graphene oxide and reduced graphene oxide) have attracted a great deal of attention and have been widely applied in the field of catalysis science owing to their exceptional physical properties and chemical tunability. This review focuses on the advances of graphene-based materials in catalytic transformation of biomass and platform molecules to value-added chemicals and biofuels, with emphasis on the development of these materials directly as catalysts and promising supports to anchor Brønsted acid sites in addition to metal nanoparticles. The state-of-the-art and future challenges of graphene-based catalysts in biomass utilization are also discussed.

A series of SBA-15-supported WO3 catalysts was prepared by impregnating silicotungstic acid on SBA-15 (HSiW-SBA-15) and subsequently calcining at different temperatures. It shows higher catalytic activity and stability than the physical mixtures of SBA-15 and WO3 in the self-metathesis of 1-butene to propene. The calcination temperature of HSiW-SBA-15 has a significant effect on its catalytic performance. The sample calcined at 700 °C gave a 1-butene conversion and a propene selectivity of 59.6% and 59.7%, respectively, at 350 °C. It was found that the metathesis of 1-butene to propene occurred via two steps. The first one was isomerization of 1-butene to 2-butene on both Brønsted and Lewis acid sites, and the second one was metathesis of 1-butene and 2-butene to propene via the formation of W-carbene species (WCHCH3, WCH2 and WCHCH2CH3). The Si–O–W–OH Brønsted acid sites play a decisive role in the formation of W-carbene species, and the pseudo-Wittig mechanism dominates the process.

A novel strategy to synthesize a size-selective catalyst consisting of a Pd-containing silica core and an outer silica shell with controllable pore size, was developed. Such intended structures were confirmed with N2 sorption, XRD, TEM and SEM. The pore sizes on the shell could be further tailored through silylation with organosilanes with variable chain lengths. This intriguing nanostructured catalyst showed a high activity in the aerobic oxidation of alcohols. Impressively, when the pores on the shell were tailored to particular sizes the catalyst exhibited size-selective catalysis, and the substrate molecules with only a slight difference in molecular size could be discriminated. This study potentially supplies a new approach for constructing size-selective catalysts.

On the basis of density functional theory including dispersion correction (ωB97XD), the thermodynamics and kinetics of the formation of polymethylbenzene intermediates in methanol to olefin conversion over zeolites with different pore sizes have been systematically computed. The agreement between the experimental and theoretical adsorption enthalpies of the several polymethylbenzenes over H-FAU reasonably validates the applied models and methods, and reveals the importance of dispersion correction in the space confinement and electrostatic stabilization of the zeolite framework. The free energies of the stepwise formation of the polymethylbenzenes show that the most favorable active hydrocarbon pool intermediates are pentamethylbenzene and hexamethylbenzene over H-BEA and H-SAPO-34, as well as tetramethylbenzene over H-ZSM-5 and H-ZSM-22. These stable polymethylbenzenes are also precursors for the formation of geminal methylated cationic intermediates on the basis of kinetic and thermodynamic analyses. The agreement of the thermodynamic and kinetic results on the favorable intermediates validates the use of Gibbs free reaction energies to estimate the primary component of the intermediates in the various zeolites. All these pore-size-dependent differences among the zeolites show their enhanced confinement effect, which is mainly influenced by the short-range electrostatic potential including stabilization and repulsion.

The methanol to hydrocarbon (MTH) process provides an efficient route for the conversion of carbon-based feedstocks into olefins, aromatics and gasoline. Still, there is room for improvements in product selectivity and catalytic stability. This task calls for a fundamental understanding of the formation, catalytic mechanism and degradation of active sites. The autocatalytic feature of the MTH process implies that hydrocarbons are active species on the one hand and deactivating species on the other hand. The steady-state performance of such species has been thoroughly studied and reviewed. However, the mechanism of formation of the initial hydrocarbon species (i.e.; the first C–C bond) and the evolution of active species into deactivating coke species have received less attention. Therefore, this review focuses on the significant progress recently achieved in these two stages by a combination of theoretical calculations, model studies, operando spectroscopy and catalytic tests.

A clear understanding of the methane formation mechanism in the initial MTO process is beneficial for the illustration of the initial C–H bond activation mechanism and the first C–C bond formation route. Thus, attempts are made here to unravel the methane formation pathway in the initial MTO process by elaborately designing experiments. It is shown that methane is generated together with formaldehyde or methoxymethyl cation by attacking the C–H bond of methanol or dimethyl ether (DME) with surface methoxy species (SMS). The reaction of DME and SMS provides strong evidence for the occurrence of C–H bond cleavage and the “methoxymethyl cation mechanism” in the initial MTO process.

Nitrogen-containing porous carbon materials are ubiquitous with a wide range of technologically important applications, including separation science, heterogeneous catalyst supports, water purification, electrochemistry, as well as the developing areas of energy generation and storage applications. To date, a variety of approaches has been developed and applied to introduce nitrogen into the carbon matrix. It is important and necessary to design and control a hierarchical porous structure and the surface chemical groups of nitrogen-containing porous carbons for their applications. In this work, we summarize and compare recently reported routes for the preparation of nitrogen-containing porous carbon materials and the effect of nitrogen groups on its applications in adsorption, electrochemistry, catalysis/catalyst supports and hydrogen storage properties.

A facile route was developed to one-step synthesize ZSM-5 hollow microspheres. It was found that their crystallization occurred at near neutral pH with the assistance of EDTA2− ions via a “crystallization in a confined space” mechanism, and the resultant sample gave an exceptional yield of aromatics with a long catalytic lifetime in the methanol-to-aromatics process.