Mn-TiO2 oxide catalyst has been studied intensively for selective catalytic reduction (SCR) of NO with NH3 due to its extraordinarily good low-temperature performance. However, the mechanism of SCR on Mn-TiO2 still remains unclear, especially with regard to the decomposition pathway of the NH2NO intermediate and the reason for the decreasing N2 selectivity with the increasing of temperature. In this work, we attempt to provide a molecular level understanding of these questions via a combination of DFT and experimental study. A complete catalytic cycle of the SCR reaction was proposed based on a model in which Mn is doped into the TiO2(101) surface by quantum-chemical DFT+U calculations. In situ DRIFTS experiments were performed to provide evidence to the important intermediates as proposed in the reaction mechanism. The doping Mn enhances NH3 adsorption and activation due to its lower conduction band. NH2NO can decompose into N2 and H2O fast via a concerted H migration step. The decreasing selectivity with rising temperature can be explained by the deep oxidation of NH3. This study provides atomic-scale insights into the catalytic cycle and the important role of doping Mn in NH3–SCR reaction on Mn-TiO2 catalysts, which is of significance for the design of high activity low-temperature SCR catalysts.

Fe/Beta@TiO2 core–shell catalysts with nanosize TiO2 thin film as the shell and small-grain Beta supporting Fe oxides as the core were controllably synthesized by a self-assembly method, and their catalytic performances were investigated for selective catalytic reduction of NOx with NH3 (NH3–SCR). It was found that TiO2 shells decrease the acid amount and weaken the acid strength of the catalyst, which could be beneficial to inhibiting the adsorption of acrolein species from covering active sites and then improving the ability of NO oxidation to NO2 during NH3–SCR. Moreover, TiO2 shells not only can prevent the deposition of coke and nitrate species from blocking the active iron sites, but also can serve as an effective barrier to suppress the active metal oxide nanoparticles from aggregating at high temperature. Therefore, Fe/Beta@TiO2 exhibits an improved thermal stability, higher propene, and H2O-tolerance.

Particulate matter and NOx emissions from diesel exhaust remains one of the most pressing environmental problems. We explore the use of hierarchically ordered mixed Fe–Ce–Zr oxides for the simultaneous capture and oxidation of soot and reduction of NOx by ammonia in a single step. The optimized material can effectively trap the model soot particles in its open macroporous structure and oxidize the soot below 400 °C while completely removing NO in the 285–420 °C range. Surface characterization and DFT calculations emphasize the defective nature of Fe-doped ceria. The isolated Fe ions and associated oxygen vacancies catalyze facile NO reduction to N2. A mechanism for the reduction of NO with NH3 on Fe-doped ceria is proposed involving adsorbed O2. Such adsorbed O2 species will also contribute to the oxidation of soot.Keywords: ceria; doping; macropores; NOx reduction; soot oxidation;

A series of Mox–Fe/beta catalysts with constant Fe and variable Mo content were synthesized and investigated for selective catalytic reduction (SCR) of NOx with NH3. It was found that the Mo0.2–Fe/beta catalyst exhibited excellent activity, N2 selectivity and preferable resistance to H2O and SO2. The Mox–Fe/beta catalysts were characterized by various analytical techniques. TEM and SEM images showed that the addition of Mo could enhance the dispersion of iron oxides. The results of NH3-TPD and Py-IR indicated that the introduction of Mo resulted in a change of Brønsted acidity, which was associated with high-temperature SCR activity. XPS and XANES results showed that the introduction of Mo resulted in a change of Fe2+ content, which determined the low-temperature activity. DFT calculations showed the strong effects of Mo on the crystal structure, charge distribution and oxygen vacancy formation energy of iron oxides, which further explained the role of Mo in the catalyst behaviors during the SCR process.

•Micro crystal α-Mn2O3 with different shapes were controllably prepared by hydrothermal method.•Soot combustion efficiency strongly depended on the crystal shapes and exposed crystal facets.•The superior reactivity of α-Mn2O3-cubic were originated from its exposed (001) facet.•The cubic α-Mn2O3 catalyst exhibited outstanding stability in soot combustion.In this work, a series of α-Mn2O3 micro crystals with different morphologies and crystal shapes were successfully prepared by hydrothermal method and has been investigated as potential soot combustion catalysts for the first time. The activity data showed that the soot combustion efficiency were markedly affected by the shape of the prepared α-Mn2O3 catalysts, among which their activity ranked as α-Mn2O3-cubic > α-Mn2O3-truncated octahedral > α-Mn2O3-octahedra. As revealed by various physicochemical characterization techniques such as XRD, SEM, HR-TEM, FT-IR, BET, H2-TPR, O2-TPD, NO- and NO + O2-TPSR, the enhanced activity as well as selectivity over α-Mn2O3-cubic is originated with the nature of the exposed α-Mn2O3 (001) surface facets, on which the higher concentration of low-coordinated surface oxygen sites facilitates the oxygen activation and improves surface redox properties, thereby accelerating the formation of the crucial intermediate i.e., NO2 formation by NO oxidation and thus promoting the overall soot combustion efficiency. Moreover, the kinetic study performed under isothermal condition provided solid evidence and proof to support that it is the exposed crystal facet, rather than surface area, to be critical to determine the catalytic performance of soot combustion. Under loose contact condition, soot combustion efficiency over best performing α-Mn2O3-cubic catalyst was further enhanced in the presence of water, CO and hydrocarbons, which are essential components in real diesel exhaust. Furthermore, the cubic α-Mn2O3 displayed excellent durability against structural collapse upon repeated recycling test and accelerated deactivation test, demonstrating its promise for the practical use in diesel soot combustion.Download high-res image (111KB)Download full-size image

•MoFe/Beta@CeO2 core-shell catalyst has been controllably synthesized by a self-assembly method.•MoFe/Beta@CeO2 shows a remarkable improvement of deNOx activity, excellent SO2 and H2O tolerance and high thermal stability.•CeO2 sheaths have inhibited the generation of ammonium sulfate and nitrate species from blocking the active sites.•CeO2 shells have served as an effective barrier to prevent the aggregation of metal oxide NPs.•The CeO2 shells promote the formation of nitrites species and NO oxidation to NO2.MoFe/Beta@CeO2 core−shell catalyst was designed with nano-size Beta supporting MoFe bimetallic oxides as the core and CeO2 thin film as the shell. The structure and physico-chemical properties of the coated and uncoated CeO2 catalysts were characterized by TEM, SEM, XRD, N2 adsorption-desorption, XPS, XANES, ICP-AES, NH3-TPD, H2-TPR and in-situ DRIFTS. The catalytic activity tests for NH3-SCR of NO indicated that the catalyst coated by CeO2 shell exhibits a remarkable improvement of deNOx activity, excellent tolerance to SO2 and H2O, as well as high thermal stability. The both chemisorbed oxygen species (O2−, O−) and specific surface area increased for the catalysts after the coating of CeO2 shells. CeO2 shells not only increase the acid amount but also improve its acid strength, which could be beneficial to improving NO oxidation to NO2 during NH3-SCR. Furthermore, there is a strong interaction among the iron oxides, molybdenum oxides and CeO2 shells. CeO2 shells can serve as an effective barrier to inhibit the active metal oxides nanoparticles from aggregating at high temperature. As a result, the coated catalyst with CeO2 thin film shows a better thermal stability than the uncoated one. What’s more, CeO2 shells can not only suppress the formation of ammonium nitrate and sulfate species blocking the active iron sites but also restrain the generation of iron sulfate, leading to a higher SO2 and H2O-tolerance. The above results demonstrate that the design of a core−shell structure catalyst is favorable for improving the performance of deNOx catalysts.Download high-res image (247KB)Download full-size image

Herein, three-dimensional ordered macropore (3DOM) x% W/Ce0.8Zr0.2O2 (x = 0.5, 0.8, 1, 3) catalysts were prepared and employed for the simultaneous removal of PM (particulate matter) and NOx from diesel engine exhaust. The contact between the solid PM and the catalyst active site was strengthened by the special 3DOM structure. 3DOM 0.8% W/Ce0.8Zr0.2O2 had superior catalytic activity with a maximum concentration of CO2 at 408 °C and nearly 100% NO conversion at 378–492 °C, and also presented high catalytic activity even under a high space velocity of 50 000 h−1. Furthermore, the stability of the catalyst was excellent even after aging at 900 °C for 5 h. The large amount of chemisorbed oxygen species, good low temperature reduction performance as well as abundant acid sites enhanced the catalytic efficiency for simultaneous PM and NOx abatement over the 3DOM 0.8% W/Ce0.8Zr0.2O2 material; this is a promising catalyst for application in exhaust purification.

Ce0.3–TiOx nanoparticle carrier was prepared by the sol–gel method, and a series of Cd–Ce–Ti nanoparticle catalysts with variable Cd contents were prepared by the means of an improved incipient-wetness impregnation. The catalysts were characterized by means of XRD, N2 adsorption–desorption analysis, SEM, TEM, NH3-TPD and in situ DRIFTS. The catalytic activities for deNOx were evaluated by NH3-SCR reaction. All these nanoparticle catalysts contain mesopores with a pore size around 7 nm, and the average particle size is 20 nm. Among the catalysts, 2 wt% Cd/Ce0.3TiOx catalyst exhibits the best NH3-SCR performance with a wide temperature window of 250–400 °C for NO conversion above 90%. Moreover, in situ DRIFTS spectra of NOx reduction over 2 wt% Cd/Ce0.3TiOx catalyst were also investigated. The results show that this reaction mainly follows the Langmuir–Hinshelwood mechanism at room temperature, while Eley–Rideal mechanism plays more important role when the reaction temperature is higher than 150 °C. The adsorbed NH3 coordinately linked to Lewis acid site is easy to react with NOx at high temperature.

Three-dimensionally ordered mesoporous Co3O4 (meso-Co3O4) and its supported Pt catalysts were synthesized for the catalytic oxidation of acetylene. All the catalysts formed mesoporous structures and possessed high surface areas of 110–122 m2 g−1. Meso-Co3O4-supported Pt catalysts exhibited highly catalytic performances, and the 0.6Pt/meso-Co3O4 catalyst gave the lowest temperature of 120 °C for acetylene oxidation. It was concluded that the ordered mesoporous structure, with plenty of structural defects, good low-temperature reducibility and the high concentration of active oxygen species were responsible for the excellent catalytic performance of 0.6Pt/meso-Co3O4.

A novel catalytic purification process SCRPF (selective catalytic reduction and particulate filter) over a 3DOM catalyst was designed and used for the simultaneous removal of PM (particulate matter) and NOx from diesel engine exhausts. It is a combination of DPF and SCR of NOx reduction technology advantages. The catalytic purification taking place over a SCRPF reactor is cost-efficient. The contact between the solid PM and the catalyst active sites is process intensified by the 3DOM unique structure. The 3DOM Ce0.85Fe0.1Zr0.05O2 catalyst gave a maximum concentration of CO2 at 415 °C for PM combustion and showed 100% NO conversion in the temperature range of 365–503 °C. The different Ce/Zr ratio and the introduction of Fe species present various Ce3+/Ce4+, abundant oxygen vacancies, excellent reducibility and sufficient acid sites in the catalyst, which are effective for the simultaneous removal of PM and NOx. The use of a low cost catalyst may be more desirable.

•CuZ-Cen catalysts using Cu-SAPO-18 zeolite as a matrix and CeO2 as a thin film were prepared.•More Cu ions and appropriate thickness of CeO2 film are important in excellent SCR activities.•CeO2 film promotes thermal stability of CuZ-Cen catalyst, especially in the steam condition.•CeO2 film has efficiently inhibited the sulfate from blocking the active sites.Cu-SAPO-18 molecular sieve was synthesized and a series of CuZ-Cen catalysts with thin CeO2 film on the external surface of Cu-SAPO-18 were prepared by the means of liquid deposition. The thickness of CeO2 film was controllably tuned, and the different film thickness significantly influenced the catalytic activities of CuZ-Cen catalysts for NH3-SCR reaction. The protection of CeO2 thin film not only inhibits the active sites from aggregating into copper oxides at high temperature, but also suppresses H2O from competitively adsorbing on the acid sites and Cu active sites over CuZ-Cen catalysts. Thus CuZ-Cen catalysts exhibit preferable resistance to H2O. Moreover, CeO2 thin film can suppress the formation and deposition of sulfate species from blocking the active sites over CuZ-Cen catalysts. It leads to that CuZ-Cen catalysts possess the higher SO2 resistance than Cu-SAPO-18.Download high-res image (235KB)Download full-size image

Size-tunable 3D rutile TiO2 spheres consisting of nanorods were controllably synthesized by adjusting the precursor hydrolysis rate. CeO2 nanoparticles were supported on TiO2 to prepare a series of Ce/Ti catalysts via an incipient wetness impregnation method. Catalytic activity tests showed that the hierarchical rutile TiO2 microspheres with a size of 1 μm containing nanorod-supported CeO2 showed excellent activity and high N2 selectivity over a wide temperature range. The novel morphology of the TiO2 nanostructures exhibits a strong interaction with CeOx species, enhancing their dispersion. The excellent catalytic activity should be mainly attributed to the enriched surface oxygen species, abundant surface acidity and high reducibility. The presence of enriched surface oxygen vacancies could facilitate the formation of active NO2 and bidentate nitrate species, leading to remarkable SCR performances. This was confirmed by in situ DRIFTS investigations.

A series of photocatalysts of three-dimensionally ordered macroporous (3DOM) TiO2-supported core–shell structured Pt@CdS nanoparticles were facilely synthesized by the gas bubbling-assisted membrane reduction-precipitation (GBMR/P) method. All the catalysts possess a well-defined 3DOM structure with interconnected networks of spherical voids, and the Pt@CdS core–shell nanoparticles with different molar ratios of Cd/Pt are well dispersed and supported on the inner wall of uniform macropores. The 3DOM structure can enhance the light-harvesting efficiency due to the increase of the distance of the light path by enhancing random light scattering. And the all-solid-state Z-scheme system with a CdS(shell)–Pt(core)–TiO2(support) nanojunction is favourable for the separation of photogenerated electrons and holes because of the vectorial electron transfer of TiO2 → Pt → CdS. 3DOM Pt@CdS/TiO2 catalysts exhibit super photocatalytic performance for CO2 reduction to CH4 under simulated solar irradiation. Among the as-prepared catalysts, the 3DOM Pt@CdS/TiO2-1 catalyst with the moderate thickness of a CdS nanolayer shell shows the highest photocatalytic activity and selectivity for CO2 reduction, e.g., its formation rate of CH4 is 36.8 μmol g−1 h−1 and its selectivity for CH4 production by CO2 reduction is 98.1%. The design and versatile synthetic approach of the all-solid-state Z-scheme system on the surface of 3DOM oxides are expected to throw new light on the fabrication of highly efficient photocatalysts for CO2 reduction to hydrocarbon.

A series of PtSnAl/SBA-15 catalysts were prepared by incipient-wetness impregnation and their catalytic performance was tested for propane dehydrogenation. The catalysts were characterized by XRF, XRD, BET, TEM, UV-vis DRS, NH3-TPD, O2-TPO, 27Al MAS-NMR, XPS and in situ Raman analyses. The addition of aluminum enhances the interaction of the Sn support and consequently stabilizes the oxidation state of Sn during the propane dehydrogenation reaction. The acid centers formed by aluminum addition show close contact with metal centers (Pt), which favors the synergistic effect of the bifunctional active centers. High catalytic performance over PtSnAl0.2/SBA-15 was obtained, and one-pass propane conversion and propene selectivity are 55.9% and 98.5%, respectively. Moreover, the in situ Raman results indicated the faster coke formation rate of PtSnAl0.4/SBA-15 than that of PtSnAl0.2/SBA-15, which may be accelerated by strong acid sites by excess aluminum addition.

A series of V–W–Ti nanoparticle catalysts with variable V doping amounts were directly synthesized by the sol–gel method, and their catalytic performances were tested for the selective catalytic reduction of NO with ammonia. The catalysts were characterized by means of XRD, Raman, BET, TEM, SEM, NH3-TPD, H2-TPR and XPS. SCR kinetic studies were conducted to understand the mechanistic features of V–W–Ti catalysts. It was found that the V0.02W0.04Ti catalyst exhibited the highest NO conversion and the lowest apparent activation energy. The characterization results showed that V was incorporated into the TiO2 framework and the redox cycle of V4+ + Ti4+ → V5+ + Ti3+ existed over the V–W–Ti catalysts. A high concentration of reducible and distorted V species could account for the excellent NH3-SCR catalytic performance of the V0.02W0.04Ti catalyst. In situ FT-IR spectroscopy was performed to investigate the mechanism of the NH3-SCR reaction over the V0.02W0.04Ti catalyst. Experimental results showed that both Lewis and Brønsted acid sites over the V0.02W0.04Ti catalyst were involved in the NH3-SCR reaction. The adsorption of nitrate species was significantly limited and the adsorbed NO2 gaseous molecules were easily formed over the V0.02W0.04Ti catalyst, which resulted in the high catalytic activity at low temperature.

A series of Cu/ZSM-5/SAPO-34 (Cu/ZS-PM) composite catalysts with fixed Cu amount and varying ZSM-5 mass fraction were synthesized using a pre-seed method, and their catalytic performances were tested for selective catalytic reduction (SCR) of NO with NH3. The catalysts were characterized by means of XRD, FT-IR, SEM, BET, UV-vis DRS, NH3-TPD, H2-TPR and in situ DRIFTS. The results indicate that the high deNOx performance of the Cu/ZS-PM-15% catalyst was due to the excellent redox property and the formation of NO2. The acidity of the catalysts was significantly influenced by the content of ZSM-5 seeds, whereas there was no obvious correlation between acid strength and NH3-SCR performance. The in situ DRIFTS spectra demonstrated that both Lewis and Brønsted acid sites are involved in the NH3-SCR reaction and the reaction on Brønsted acid sites is more active than that on Lewis acid sites. NO2 is a primary intermediate following NO adsorption on Cu/ZS-PM catalysts, which may promote a “fast” SCR reaction at low temperature.

A series of PtSn/SBA-15 catalysts with different metal loading amounts were prepared by an incipient-wetness impregnation method and their catalytic performances were tested for propane dehydrogenation. The catalysts were characterized by means of XRD, BET, TEM, UV-Vis DRS, O2-TPO, H2-TPR, XPS and Raman spectroscopy. The catalytic activity for propane dehydrogenation increases with an increase in the loading amount of metal, and it remained stable when the Pt loading amount reached 1 wt%. It is found that the state of Pt or Sn in the catalysts varies with changes in metal loading. When the loading of Pt and Sn exceed a certain amount (Pt 1 wt% and Sn 2 wt%), the state of Pt and Sn changes apparently with the more oxidative Pt and more reduced Sn. The changes of the state of Pt and Sn influence the catalytic performance of these catalysts. Moreover, the size of the PtSn nanoparticles increases with increasing amounts of Pt and Sn, which also results in a change in the catalytic performance. The Pt1Sn2/SBA-15 catalyst shows the highest initial activity, which results from an increased amount of active sites, the high dispersion of PtSn nanoparticles and the favorable state of the Pt and Sn species.

LaFeO3 was used to improve the hydrogen storage properties of MgH2. The MgH2+20 wt.%LaFeO3 composite was prepared by ball milling method. The composite could absorb 3.417 wt.% of hydrogen within 21 min at 423 K while MgH2 only uptaked 0.977 wt.% hydrogen under the same conditions. The composite also released 3.894 wt.% of hydrogen at 623 K, which was almost twice more than MgH2. The TPD measurement showed that the onset dissociation temperature of the composite was 570 K, 80 K lower than the MgH2. Based on the Kissinger plot analysis of the composite, the activation energy Edes was estimated to be 86.69 kJ/mol, which was 36 kJ/mol lower than MgH2. The XRD and SEM results demonstrated that highly dispersed LaFeO3 could be presented in MgH2, benefiting the reduction of particle size and also acting as an inhibitor to keep the particles from clustering during the ball-milled process.Temperature-pressure-desorption curves of the MgH2+20 wt.%LaFeO3 composite and MgH2

A series of catalysts of three-dimensionally ordered macroporous (3DOM) Ce0.8Zr0.2O2-supported gold nanoparticles with controllable sizes were successfully synthesized by the facile method of gas bubbling-assisted membrane reduction (GBMR). All the catalysts possess well-defined 3DOM structures, which consist of interconnected networks of spherical voids, and the Au nanoparticles are well dispersed and supported on the inner wall of the uniform macropore. The relationship between Au particle sizes and the ability to adsorb and activate oxygen was characterized by means of O2-TPD and XPS. The results show that the active oxygen species (O−) and gold ions with oxidation state of Au+ are essential for soot oxidation reaction. 3DOM Au0.04/Ce0.8Zr0.2O2catalyst with Au particle size of 2–3 nm has the strong capability of adsorption and activation of oxygen. Thus, it exhibits super-catalytic activity for diesel soot oxidation, especially at low temperature. The reaction pathways of catalytic soot oxidation in the presence or absence of NO can be outlined as follows: at low temperature (<250 °C), the catalytic performance of supported Au catalyst is dependent on the Au particle sizes. At relatively high temperature (>250 °C), the catalytic activity is strongly related to the NO gas, because NO2 derived from NO oxidation is used as intermediate to catalyze soot oxidation.

SBA-15 supported Mo catalysts (Moy/SBA-15) were prepared by an ultrasonic assisted incipient-wetness impregnation method. The physical and chemical properties of the catalysts were characterized by means of N2-adsorption-desorption, XRD, TEM, UV-Vis, Raman, XANES and H2-TPR. The results showed that a trace amount of MoO3 was produced on high Mo content samples. Turn-over frequency (TOF) and product selectivity are dependent on the molybdenum content. Both Mo0.75/SBA-15 and Mo1.75/SBA-15 catalysts give the higher catalytic activity and the selectivity to the total aldehydes for the selective oxidation of C2H6. At the reaction temperature of 625 °C, the maximum yield of aldehydes reached 4.2% over Mo0.75/SBA-15 catalyst. The improvement of the activity and selectivity was related with the state of MoOx species.Among the series Mox/SBA-15 catalysts, the low Mo loading is beneficial to the formation of isolated tetra-coordination molybdenum species, these species are beneficial to the formation of total aldehydes in the selective oxidation of C2H6.Download full-size image

A series of meso-microporous Cu-SAPO-34 catalysts were successfully synthesized by a one-pot hydrothermal crystallization method, and these catalysts exhibited excellent NH3-SCR performance at low temperature. Their structure and physic chemical properties were characterized by means of X-ray diffraction patterns (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), N2 sorption-desorption, nuclear magnetic resonance (NMR), Inductively Coupled Plasma-Atomic Emission spectrometer (ICP-AES), X-ray absorption spectroscopy (XPS), Temperature-programmed desorption of ammonia (NH3-TPD), Ultraviolet visible diffuse reflectance spectroscopy (UV-Vis DRS) and Temperature programmed reduction (TPR). The analysis results indicate that the high activities of Cu-SAPO-34 catalysts could be attributed to the enhancement of redox property, the formation of mesopores and the more acid sites. Furthermore, the kinetic results verify that the formation of mesopores remarkably reduces diffusion resistance and then improves the accessibility of reactants to catalytically active sites. The 1.0-Cu-SAPO-34 catalyst exhibited the high NO conversion (> 90%) among the wide activity temperature window in the range of 150–425°C.Download high-res image (113KB)Download full-size image

Highly ordered mesoporous NiMoO4 material was successfully synthesized using mesoporous silica KIT-6 as hard template via vacuum nanocasting method. The structure was characterized by means of XRD, TEM, N2 adsorption-desorption, Raman and FT-IR. The mesoporous NiMoO4 with the coexistence of α-NiMoO4 and β-NiMoO4 showed well-ordered mesoporous structure, a bimodal pore size distribution and crystalline framework. The catalytic performance of NiMoO4 was investigated for oxidative dehydrogenation of propane. It is demonstrated that the mesoporous NiMoO4 catalyst with more surface active oxygen species showed better catalytic performance in oxidative dehydrogenation of propane in comparison with bulk NiMoO4.The vacuum nanocasting method was employed to enhance the capillary force. Ordered mesoporous NiMoO4 material was successfully synthesized. Ordered mesoporous NiMoO4 shows better catalytic performance for ODHP than bulk NiMoO4.Download full-size image

•A novel Mo-incorporated KIT-6 catalyst was synthesized by a one-pot co-assembly method.•Mo-KIT-6 gave a high concentration of framework-isolated MoOx and anchored them firmly.•In situ Raman results showed that Mo-KIT-6 has a good redox ability to regenerate the reduced MoOx.•In situ Raman results showed that Mo-KIT-6 has strong carbon deposition resistance and stability.•The maximal yield of acrolein reached 25.9% over 0.25 K/0.1Mo-KIT-6 catalyst.A series of novel molybdenum-incorporated mesoporous silica catalysts (Mo-KIT-6) were successfully synthesized by a one-pot co-assembly method. For comparison, corresponding mesoporous KIT-6-supported molybdena catalysts (Mo/KIT-6) were also prepared by the impregnation method. For Mo-KIT-6 catalysts, the molybdenum was substituted into the framework of the KIT-6 support, which contributed to obtaining high concentrations of highly dispersed and isolated active sites and to anchoring the active sites firmly. We determined the identity of the active sites of Mo-KIT-6 catalysts as Mo oxide units with more anchoring MoOSi bonds than in the corresponding Mo/KIT-6 at elevated temperature. The Mo-KIT-6 catalysts possess appropriate redox properties, high stability, and a strong ability to resist carbonaceous species formation, which was confirmed by in situ UV Raman results. Furthermore, the addition of K to Mo-KIT-6 catalyst further promoted the formation of acrolein, and the maximum single-pass yield of acrolein reached 25.9%.Download high-res image (168KB)Download full-size image

•Simultaneous removal of PM and NOx is performed on a single 3DOM catalyst.•3DOM Ce0.8Mn0.1Zr0.1O2 shows excellent activities for simultaneous abatement.•Doped Mn improves surface reducibility and produces abundant of oxygen vacancies.•The introduction of Mn promotes the adsorption and activation of NH3.A novel catalytic purification process over a 3DOM catalyst, called SCRPF (Selective Catalytic Reduction and Particulate Filter), was designed and employed for the simultaneous removal of PM (particulates matter) and NOx from diesel engine exhausts. This process combines the advantages of the DPF and SCR of NOx reduction processes. The catalytic purification process occurring over a SCRPF reactor is cost-efficient. The contact between solid PM and the catalyst active site has been intensified by the unique 3DOM structure. 3DOM Ce0.8Mn0.1Zr0.1O2 catalyst provided the maximum concentration of CO2 at 402 °C for PM combustion and showed excellent NH3-SCR performance in the 374–512 °C temperature range. The specific 3DOM architecture, high Ce3+/Ce4+ ratio and amount of chemisorbed oxygen species, good low-temperature reducibility as well as the abundant of acid sites are responsible for the excellent catalytic efficiency of Ce0.8Mn0.1Zr0.1O2 sample used for the simultaneous removal of PM and NOx from diesel engines. The use of an inexpensive catalyst may make the practical application of this process more advantageous.The novel SCRPF combining catalyst path is an efficient and economical way to purify PM and NOx from diesel engines. 3DOM Ce0.8Mn0.1Zr0.1O2 catalyst possesses unique macroporous structure, abundant oxygen, low-temperature reducibility and proper acid site. It gives the surprising highly catalytic activity for the simultaneous removal of PM and NOx.Download high-res image (99KB)Download full-size image

Selective catalytic reduction technology using NH3 as a reducing agent (NH3-SCR) is an effective control method to remove nitrogen oxides. TiO2-supported vanadium oxide catalysts with different levels of Ce and Sb modification were prepared by an impregnation method and were characterized by X-ray diffractometer (XRD), Brunauer–Emmett–Teller (BET), Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS), Raman and Hydrogen temperature-programmed reduction (H2-TPR). The catalytic activities of V5CexSby/TiO2 catalysts for denitration were investigated in a fixed bed flow microreactor. The results showed that cerium, vanadium and antimony oxide as the active components were well dispersed on TiO2, and the catalysts exhibited a large number of d–d electronic transitions, which were helpful to strengthen SCR reactivity. The V5CexSby/TiO2 catalysts exhibited a good low temperature NH3-SCR catalytic activity. In the temperature range of 210 to 400°C, the V5CexSby/TiO2 catalysts gave NO conversion rates above 90%. For the best V5Ce35Sb2/TiO2 catalyst, at a reaction temperature of 210°C, the NO conversion rate had already reached 90%. The catalysts had different catalytic activity with different Ce loadings. With the increase of Ce loading, the NO conversion rate also increased.NO conversion as a function of reaction temperature over V5CexSby/TiO2 catalysts with different Ce and Sb loadings.A series of V5CexSby/TiO2 catalysts are tested in the NH3-SCR of NO. All vanadium–titanium based catalysts have good low temperature NH3-SCR activity with different Ce and Sb loadings. When the reaction temperature is at 225°C, NO conversion can reach 90% over all the catalysts. With the increasing of the Ce loading, the conversion of NO increases. At 225–400°C, NO conversion can maintain above 90% for all V5CexSby/TiO2 catalysts with a wide temperature window. Addition of antimony (2 wt.%) leads to improving a low temperature NH3-SCR activity. V5Ce35Sb2/TiO2 catalyst exhibits the best catalytic activity for the removal of NO. At 210°C, NO conversion has already reached 90%. The results suggest that the addition of cerium and antimony can especially improve the catalytic activity of the SCR reaction at low temperature.Download full-size image

A series of PtSnAl/SBA-15 catalysts were prepared by incipient-wetness impregnation and their catalytic performance was tested for propane dehydrogenation. The catalysts were characterized by XRF, XRD, BET, TEM, UV-vis DRS, NH3-TPD, O2-TPO, 27Al MAS-NMR, XPS and in situ Raman analyses. The addition of aluminum enhances the interaction of the Sn support and consequently stabilizes the oxidation state of Sn during the propane dehydrogenation reaction. The acid centers formed by aluminum addition show close contact with metal centers (Pt), which favors the synergistic effect of the bifunctional active centers. High catalytic performance over PtSnAl0.2/SBA-15 was obtained, and one-pass propane conversion and propene selectivity are 55.9% and 98.5%, respectively. Moreover, the in situ Raman results indicated the faster coke formation rate of PtSnAl0.4/SBA-15 than that of PtSnAl0.2/SBA-15, which may be accelerated by strong acid sites by excess aluminum addition.

A series of photocatalysts of three-dimensionally ordered macroporous (3DOM) TiO2-supported core–shell structured Pt@CdS nanoparticles were facilely synthesized by the gas bubbling-assisted membrane reduction-precipitation (GBMR/P) method. All the catalysts possess a well-defined 3DOM structure with interconnected networks of spherical voids, and the Pt@CdS core–shell nanoparticles with different molar ratios of Cd/Pt are well dispersed and supported on the inner wall of uniform macropores. The 3DOM structure can enhance the light-harvesting efficiency due to the increase of the distance of the light path by enhancing random light scattering. And the all-solid-state Z-scheme system with a CdS(shell)–Pt(core)–TiO2(support) nanojunction is favourable for the separation of photogenerated electrons and holes because of the vectorial electron transfer of TiO2 → Pt → CdS. 3DOM Pt@CdS/TiO2 catalysts exhibit super photocatalytic performance for CO2 reduction to CH4 under simulated solar irradiation. Among the as-prepared catalysts, the 3DOM Pt@CdS/TiO2-1 catalyst with the moderate thickness of a CdS nanolayer shell shows the highest photocatalytic activity and selectivity for CO2 reduction, e.g., its formation rate of CH4 is 36.8 μmol g−1 h−1 and its selectivity for CH4 production by CO2 reduction is 98.1%. The design and versatile synthetic approach of the all-solid-state Z-scheme system on the surface of 3DOM oxides are expected to throw new light on the fabrication of highly efficient photocatalysts for CO2 reduction to hydrocarbon.

A novel catalytic purification process SCRPF (selective catalytic reduction and particulate filter) over a 3DOM catalyst was designed and used for the simultaneous removal of PM (particulate matter) and NOx from diesel engine exhausts. It is a combination of DPF and SCR of NOx reduction technology advantages. The catalytic purification taking place over a SCRPF reactor is cost-efficient. The contact between the solid PM and the catalyst active sites is process intensified by the 3DOM unique structure. The 3DOM Ce0.85Fe0.1Zr0.05O2 catalyst gave a maximum concentration of CO2 at 415 °C for PM combustion and showed 100% NO conversion in the temperature range of 365–503 °C. The different Ce/Zr ratio and the introduction of Fe species present various Ce3+/Ce4+, abundant oxygen vacancies, excellent reducibility and sufficient acid sites in the catalyst, which are effective for the simultaneous removal of PM and NOx. The use of a low cost catalyst may be more desirable.

Size-tunable 3D rutile TiO2 spheres consisting of nanorods were controllably synthesized by adjusting the precursor hydrolysis rate. CeO2 nanoparticles were supported on TiO2 to prepare a series of Ce/Ti catalysts via an incipient wetness impregnation method. Catalytic activity tests showed that the hierarchical rutile TiO2 microspheres with a size of 1 μm containing nanorod-supported CeO2 showed excellent activity and high N2 selectivity over a wide temperature range. The novel morphology of the TiO2 nanostructures exhibits a strong interaction with CeOx species, enhancing their dispersion. The excellent catalytic activity should be mainly attributed to the enriched surface oxygen species, abundant surface acidity and high reducibility. The presence of enriched surface oxygen vacancies could facilitate the formation of active NO2 and bidentate nitrate species, leading to remarkable SCR performances. This was confirmed by in situ DRIFTS investigations.