Active Temperature Window Research Articles

Ternary MnCoVOx catalysts with remarkable deNOx performance: Dual acid-redox sites control strategy

How to widen the active temperature window of metal oxide catalysts for abatement of NOx is urgent for their real application. Herein, a series of ternary MnCoVOx metal oxide catalysts with outstanding denitration performance were designed via a simple dual acid-redox sites tuning strategy, which is to inhibit the redox ability properly and enhance the acidity to make the catalyst exerts the optimum. The Mn0.50Co0.49V0.01Ox catalyst after vanadium tuning exhibited superior catalytic performance, achieving > 80% NOx conversion over a wide temperature window (162−508 °C) under the humid reaction condition, the selectivity of N2 > 85% up to 510 °C, and also displayed enhanced SO2 tolerance. Compared with the commercial Cu-SSZ-13 catalyst, the ternary MnCoVOx catalysts showed comparable activity but better sulfur resistance. Thereby, the easy-synthesized and low-cost ternary metal oxides based on the dinuclear active sites tuning strategy pave a way for designing superior denitration catalysts for practical applications.

Improving NH3-SCR denitrification performance over WaCo0.4TiOx catalysts: Effect of surface acidity due to W addition on low-temperature and high-temperature activity

A serial of WaCo0.4TiOx catalysts (a = 0.04, 0.06, 0.08, 0.10) was synthesized by sol-gel method, which exhibited high NH3-SCR denitrification performance in a wide activity temperature window. W0.08Co0.4TiOx achieve best SCR activity (over 90% NO conversion) at 190–430 °C and good resistance to H2O/SO2. Various characterizations were used to investigate the influence of W doping on physicochemical property of these catalysts. Especially, in-situ DRIFTS were used to evaluate the type of acid sites, NOx adsorption, the reactivity of surface adsorption species, and the influences of H2O/SO2 on adsorption of NOx and NH3. The doping of W enhanced the acidity and weakened the oxidation capacity of WaCo0.4TiOx, but higher surface acidity, especial more Brønsted acid sites, can compensate for the effect of the decrease in the oxidation capacity on low-temperature activity. The optimal activity over W0.08Co0.4TiOx can be derived from the synergistic effect of surface acidity and oxidation performance.

Effect of MnOx/α-Fe2O3 Prepared from Goethite on Selective Catalytic Reduction of NO with NH3

A low-cost goethite and manganese acetate were used to prepare a MnOx/α-Fe2O3 composite catalyst by simple impregnation method for novel high-efficiency selective catalytic reduction (SCR) of NO with NH3, and its denitration performance of composite catalyst under different conditions was investigated in a thermal fixed-bed catalytic reaction system. The results showed that MnOx/α-Fe2O3 with Mn/Fe molar ratio of 0.1 and calcination temperature of 400 °C had the best low-temperature catalytic activity and wider reaction temperature window compared with α-Fe2O3. It achieved over 90% NO conversion efficiency with a space velocity of 72,000 h−1 at 200~350 °C and possessed a good resistance of H2O and SO2. Characterization by XRD, BET, H2-TPR, and NH3-TPD revealed that the main reason for the high catalytic activity of MnOx(0.1)/α-Fe2O3(400) was that the addition of Mn changed phase types of catalyst and valence composition of Fe, resulting in a larger specific surface area, more acidic sites, and higher redox performance.

Boosting low-temperature selective catalytic reduction of NO with NH3 of V2O5/TiO2 catalyst via B-doping

A series of B-doped V2O5/TiO2 catalysts has been prepared the by sol-gel and impregnation methods to investigate the influence of B-doping on the selective catalytic reduction (SCR) of NOx with NH3. X-ray diffraction, Brunauer-Emmett-Teller specific surface area, scanning electron microscope, X-ray photoelectron spectroscopy, temperature-programmed reduction of H2 and temperature-programmed desorption of NH3 technology were used to study the effect of the B-doping on the structure and NH3-SCR activity of V2O5/TiO2 catalysts. The experimental results demonstrated that the introduction of B not only improved the low-temperature SCR activity of the catalysts, but also broadened the activity temperature window. The best SCR activity in the entire test temperature range is obtained for VTiB2.0 with 2.0% doping amount of B and the NOx conversion rate is up to 94.3% at 210 °C. The crystal phase, specific surface area, valence state reducibility and surface acidity of the active components for the as-prepared catalysts are significantly affected by the B-doping, resulting in an improved NH3-SCR performance. These results suggest that the V2O5/TiO2 catalysts with an appropriate B content afford good candidates for SCR in the low temperature window.

Selective catalytic reduction of NOx by hydrogen over PtIr/TiO2 catalyst

PtIr/TiO2 catalyst was prepared and investigated for the selective catalytic reduction of NOx by H2 (H2-SCR) in the presence of O2. It was found that PtIr/TiO2 exhibited higher H2-SCR activity as well as wider activity temperature window than Pt/TiO2 and Ir/TiO2 catalysts, and the optimum mass ratio of Pt/Ir was 1:1. Characterization of the catalyst showed that metallic Pt and Ir were generated on PtIr/TiO2, both of which were favorable active sites in H2-SCR process. In situ DRIFTS studies showed that more NOx species, NH3 and NH4+ species were formed on PtIr/TiO2. All of these lead to the superior catalytic activity of PtIr/TiO2 catalyst.

Converting Poisonous Sulfate Species to an Active Promoter on TiO2 Predecorated MnOx Catalysts for the NH3-SCR Reaction.

MnOx-based catalysts possess excellent low-temperature NH3 selective catalytic reduction (NH3-SCR) activity, but the poor SO2/sulfate poisoning resistance and the narrow active-temperature window limit their application for NOx removal. Herein, TiO2 nanoparticles and sulfate were successively introduced into MnOx-based catalysts to modulate the NH3-SCR activity, and the active-temperature window (NO conversion above 80%, T80) was significantly broadened to 100-350 °C (SO42--TiO2@MnOx) compared to that of the pristine MnOx catalyst (ca. T80: 100-268 °C). Combined with advanced characterizations and control experiments, it was clearly shown that the poisonous effects of sulfate on the MnOx catalyst could be efficiently inhibited in the presence of TiO2 species due to the interaction between sulfate and TiO2 to form a solid superacid (SO42--TiO2) species as NH3 adsorption sites for the low-temperature process. Furthermore, such solid superacid (SO42--TiO2) species could weaken the redox ability to inhibit the excessive oxidation of NH3 and thus enhance the high-temperature activity significantly. This work not only puts forward the TiO2 predecoration strategy that converts sulfate to a promoter to broaden the active temperature window but also experimentally proves that the requirement of redox ability and acidity in the MnOx-based NH3-SCR catalyst was dependent on the reaction temperature range.

Improvement of Al2O3 on the multi-pollutant control performance of NOx and chlorobenzene in vanadia-based catalysts

We compared the influences of Al2O3 and SiO2 on a traditional V2O5–MoO3/TiO2 for the simultaneous removal of NOx and chlorobenzene (CB). The Al2O3 doping catalyst considerably broadens the active temperature window with higher NOx reduction and CB oxidation efficiencies than the SiO2 doping one and the V2O5–MoO3/TiO2. Furthermore, its resistance to SO2 was preserved and the quantities of polychlorinated byproducts also decreased. The increase in activity at low temperatures could be due to the promotion of vanadia reducibility via interactions between V2O5 and Al2O3. Moreover, the high temperature activity could be due to the additional surface acidities provided by Al2O3, in which the Lewis acid sites played the predominant role in both NH3 adsorptions and CB de-chlorination compared to the Brønsted acid sites. Finally, we proposed that Al2O3 is an effective addition for vanadia-based catalyst in NOx and CB simultaneous removal from stationary sources.

Enhancing low‐temperature SCR deNOx MnCe catalyst based on rice husk char by KOH and H3PO4 activation

AbstractBACKGROUNDIt is of great significance industrially to find cheap materials as low‐temperature selective catalytic reduction (SCR) catalyst support. Pyrolyzed rice husk char (RC) is not only cheap, but also has the characteristics of high porosity, large SSA and good adsorption. Therefore, there is emerging interest in RC as an SCR support. The present contribution is a comparative study of low‐temperature SCR manganese–cerium (MnCe) catalysts based on RC activated by potassium hydroxide (KOH) and phosphoric acid (H3PO4), revealing the different mechanisms of improvement in catalytic performance.RESULTSMn‐Ce/RCK (catalyst of MnCe loaded on KOH activated RC) has a wider activity temperature window in the range 120–260 °C, while Mn‐Ce/RCP (catalyst of MnCe loaded on H3PO4 activated RC) can reach the highest NO conversion of 97% at 240 °C.CONCLUSIONSN2 adsorption–desorption, Fourier transform infrared (FTIR), X‐ray diffraction (XRD), NH3‐temperature programmed desorption (TPD) and X‐ray photoelectron spectroscopy (XPS) were used to characterize and analyze their catalytic performance. The N2 adsorption–desorption and NH3‐TPD showed that Mn‐Ce/RCK has a larger SSA and more acid sites than those of Mn‐Ce/RC and Mn‐Ce/RCP. XRD indicated that Mn‐Ce/RCP has a better dispersion than that of Mn‐Ce/RCK. FTIR showed that Mn‐Ce/RCP had more oxygen (O)‐containing functional groups. The XPS revealed that Mn‐Ce/RCP has higher ratios of Mn4+, Ce3+ and Oβ. © 2021 Society of Chemical Industry (SCI).

Selective catalytic oxidation of ammonia over AMn2O5 (A = Sm,Y,Gd) and reaction selectivity promotion through Nb decoration

Ammonia selective catalytic oxidation (NH3-SCO) represents an efficient technique to control the slip NH3, which has recently been found to be a significant factor in the formation of haze. It is highly desirable to have an NH3-SCO catalyst with low cost, robust activity, high selectivity and wide operation temperature window at the same time. In this work, we have developed a series of precious-metal-free mullite based AMn2O5 (A = Sm, Y, Gd) catalysts with better NH3-SCO performance than 1.2 %Pt/γ-Al2O3 samples, among which SmMn2O5 achieves the best low temperature activity with 97% of NH3 conversion at 180 °C. Combining in situ diffuse reflectance infrared Fourier transform spectroscopy analysis and density functional theory calculation, it was revealed that the rate determining step on SmMn2O5 was the formation of N2 from adsorbed –HNO and –NH groups. Based on this, the reaction selectivity of AMn2O5 was further improved by the surface Nb2O5 decoration. The promotional effect can be attributed to the enhanced catalyst’s attraction to the lone-pair electron of N atoms, which increases the –NH group amount and facilitates the reaction between –HNO and –NH groups to produce N2. Among all modified AMn2O5 catalysts, 5.0 %Nb2O5/SmMn2O5 stands out with a NH3 conversion of 96% and N2 selectivity of 68% at 180 °C, and a wide temperature window of 180 ~ 250 °C, that represents the best overall performance reported non-noble catalysts for NH3-SCO application.

Toward rational design of a novel hierarchical porous Cu-SSZ-13 catalyst with boosted low-temperature NOx reduction performance

Nitrogen oxide (NOx), one of the main air pollutants exhausted from diesel vehicles, is harmful to the environment and human health and has been selectively catalytically reduced to N2 by Cu-exchanged zeolites with chabazite structures (CHA, Cu-SSZ-13). Unfortunately, the conventional Cu-SSZ-13 catalyst still has disadvantages in real applications, such as diffusion limits and micropore blocking due to formation of ammonium sulfates, especially at low reaction temperatures. Here, a highly crystalline hierarchical porous Cu-SSZ-13 zeolite (termed Cu-SSZ-13-HP) with enriched mesopores was rationally designed and prepared via a dual-template method for the first time. The novel Cu-SSZ-13-HP catalyst displayed boosted low-temperature activity (temperature of 70% conversion below 150 °C) and broadened active temperature window (between 175 and 500 °C, NOx conversion above 90%) compared with conventional Cu-SSZ-13 with only micropores. Importantly, Cu-SSZ-13-HP also exhibited superior hydrothermal stability and enhanced sulfur dioxide (SO2) tolerance, even when exposed to 100 ppm of SO2 for 4 h. The in situ diffuse reflectance infrared Fourier transform spectroscopy revealed that the NH3 selective catalytic reduction reaction might conform to the Langmuir–Hinshelwood mechanism in which ammonia (NH3) and NOx were activated by the acid and redox sites, respectively. The Cu-SSZ-13-HP catalyst developed by the dual-template strategy might be a good candidate for low-temperature reduction of NOx exhaust from diesel vehicles.

Influence of CePO4 with different crystalline phase on selective catalytic reduction of NOx with ammonia

A series of cerium phosphate catalysts with different crystal phases were synthesized by hydrothermal method and co-precipitation method. Hexagonal cerium phosphate (CePO4-H) shows better NH3-SCR denitration activity than monoclinic cerium phosphate (CePO4-M) and mixed phases of CePO4-H and CePO4-M. Moreover, CePO4-H also exhibits excellent activity stability with stream time and cycling stability. Various characterizations were carried out to explain the effects of different crystal phases of CePO4 on the activity. Among these catalysts, CePO4-H has much stronger surface acidity that is conducive to the adsorption and activation of NH3, and more surface adsorbed oxygen species that can effectively improve SCR activity. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were performed to investigate the adsorption and reaction of NH3 and NOx on CePO4-H and CePO4-M, and the results suggest that the better activity over CePO4-H follows mainly the Eley–Rideal mechanism in the activity temperature window (300–500 °C) with 100% NO conversion.

HC-SCR system combining Ag/Al2O3 and Pd/Al2O3 catalysts with resistance to hydrothermal aging for simultaneous removal of NO, HC, and CO

A combined Ag/Al2O3 and Pd/Al2O3 catalyst was investigated for the selective catalytic reduction (SCR) of NOx by H2-assisted C3H6 in the presence of excessive O2. The coexistent H2 significantly lowered the active temperature window of the de-NOx reaction because of the enhanced partial oxidation of C3H6 and NO oxidation to NO2. A low Ag loading of 1 wt% exhibited better de-NOx performance than that attained using 2 wt% Ag. Although Ag/Al2O3 exhibited a high resistance to hydrothermal aging, a high reaction temperature (>500 °C) was required to oxidize CO and C3H6 completely. In contrast to Ag/Al2O3, Pd/Al2O3 suppressed C3H6 and CO slip at relatively low temperatures, and a complete oxidation of C3H6 and CO was achieved at 195–275 °C and 240–275 °C, respectively, under varying SCR conditions and Pd contents (0.5–1.5 wt%); however, 30% de-NOx performance in a narrow temperature window of 210–240 °C was attained. The best configuration was found to be a sequential arrangement of 1Ag/Al2O3 followed by 1Pd/Al2O3, which enabled the reduction of NOx, C3H6, CO, and H2 over wide reaction temperatures, unlike the stand-alone configuration. In this configuration, the reacted NOx was reduced to N2 with negligible formation of by-products, even after hydrothermal aging.

Influence of Copper Locations on Catalytic Properties and Activities of Cu/SAPO-34 in C3H6-SCR

Herein, Cu-modified SAPO-34 catalysts with various copper loadings are synthesized via a pH-controlled ion-exchange method. Cu exists predominantly as isolated cations at lower loadings, located at octahedrally coordinated sites in the ellipsoidal cavity of SAPO-34 zeolites, while CuO is gradually generated on the external surface at higher loadings. Our results reveal that the isolated Cu cations are the active sites for C₃H₆-SCR. The presence of CuO species enhances the C₃H₆ activation ability of the catalysts, which thus, improves the C₃H₆-SCR performance at medium and low temperatures (below 400 °C). At high temperatures, however, the formation of CuO accelerates the nonselective oxidation of C₃H₆ and causes activity decline. These findings suggest that the active temperature window for hydrocarbons-selective catalytic reduction (HC-SCR) reactions over Cu/SAPO-34 catalysts can be tailored by tuning the proportion of various copper species to fit the need in real applications, which provide new insights into understanding and designing highly efficient Cu-based zeolite catalysts.

Impact of toluene poisoning on MnCe/HZSM-5 SCR catalyst

Increasing attentions have been drawn towards the simultaneous removal of toluene in current existing NH3-SCR unit. The development of dual-functional catalysts and the understanding of impact induced by toluene addition are momentous but lacking. Herein, a well-reported MnOx-CeO2 catalyst was chosen as active phase to assess the role of HZSM-5 in this simultaneous removal process. HZSM-5 was found to supply more acid sites especially Lewis acid on the MnOx-CeO2 catalyst. A MnCe/HZSM-5 catalyst with a SiO2/Al2O3 molar ratio of 25 delivered a broad active temperature window of 200–400 °C with NO conversion > 80% and possessed a stable N2 selectivity > 96% in NH3-SCR reaction. Also, it was able to maintain above 60% of toluene conversion in the range of 200–400 °C. More Lewis acid sites, together with abundant Mn4+, Ce3+ and active surface oxygen that formed via the interaction between Mn4+/Mn3+ and Ce4+/Ce3+ (Mn3+ + Ce4+ ↔ Mn4+ + Ce3+), contributed to the superior catalytic performance of MnCe/HZSM-5 with lower SiO2/Al2O3 ratio. A reversible catalyst deactivation in NH3-SCR induced by toluene was found. Toluene was prone to reacting with NH3 forming nitriles, which infringed the active sites and decreased the available coordinated NH3 on Lewis acid sites. In addition, the suppression of NO oxidation to NO2 that decreasing the percentage of “fast SCR” process, and the inhibition of NH3 activation to NH2 species also contributed to the lower SCR activity in the presence of toluene over MnCe/HZSM-5.

Preparation of Metal-Incorporated SAPO-34 catalysts and their Catalytic Performance in Selective Catalytic Reduction of Nitric Oxide

Abstract Metal-incorporated SAPO-34 catalysts were prepared by one-step hydrothermal method. Effects of various parameters including the types of metal ions, Cu2+ sources, structure directing agents (SDAs), hydrothermal temperature and time on catalyst activity of the metal-incorporated SAPO-34 catalysts were investigated. Three types of metal-incorporated SAPO-34 catalysts (Cu/SAPO-34, Fe/SAPO-34 and Mn/SAPO-34) were successfully obtained. Compared with Fe/SAPO-34 and Mn/SAPO-34 catalysts, Cu/SAPO-34 catalyst revealed complete cubic-like microstructure, wide active temperature window and high conversion rate in selective catalytic reduction (SCR) of nitric oxide. After defined Cu2+ was the favorable active site of SAPO-34 catalyst, the effects of four Cu2+ sources on SCR performance were further investigated, and found Cu2+ sources did not produce significant influence on nitric oxide conversion rates. SDAs determined the formation of Cu/SAPO-34 catalyst, and the Cu/SAPO-34 catalyst adopting tetraethylenepentamine (TEPA) as SDA could maintain higher crystal integrity and active sites, which were in favor of the SCR reaction. Moreover, hydrothermal temperature and time had great influences on the formation of Cu/SAPO-34 catalyst. When the hydrothermal temperature was higher than 150 oC and the hydrothermal time was longer than 3 days, the Cu/SAPO-34 catalyst with a cubic-like structure and high catalyst activity could be obtained.

Promotional effect of ion-exchanged K on the low-temperature hydrothermal stability of Cu/SAPO-34 and its synergic application with Fe/Beta catalysts

Kions were introduced onto Cu/SAPO-34 catalysts via the ion-exchange process in order to improve their stability under low-temperature hydrothermal aging. The changes in structure and copper-species contents of these catalysts upon hydrothermal aging were probed in order to investigate their effects on selective catalytic reduction (SCR) activity. For the fresh Cu/SAPO-34 catalysts, K ions had little influence on the chabazite framework but effected their acidities by exchanging with acid sites. After hydrothermal aging, the structural integrity and amount of active sites decreased on pure Cu/SAPO-34. While the K-loaded catalysts showed improved chabazite structure, acidity, and active site conservation with increasing K loading. However, although the 0.7 wt% K catalyst maintained the same crystallinity, active site abundance, and low-temperature SCR activity as the fresh catalyst upon aging, an apparent decrease in SCR activity at high temperature was observed because of the inevitable decrease in the number of Bronsted acid sites. To compensate for the activity disadvantage of K-loaded Cu/SAPO-34 at high temperature, Fe/Beta catalysts were co-employed with K-loaded Cu/SAPO-34, and a wide active temperature window of SCR activity was obtained. Thus, our study reveals that a combined system comprising Fe/Beta and K-loaded Cu/SAPO-34 catalysts shows promise for the elimination of NOx in real-world applications.

Boosting the Alkali/Heavy Metal Poisoning Resistance for NO Removal by Using Iron-Titanium Pillared Montmorillonite Catalysts

It is still a big challge to improve the alkali and heavy metal resistance of deNOx catalysts for selective catalytic reduction (SCR) of NOx with NH3. In this study, a novel catalyst developed by pillaring montmorillonite with iron and titanium (Fe-Ti-MMT) was proposed. It is quite interesting that high resistance to alkaline and heavy metals has been demonstrated by using Fe-Ti-MMT catalysts. It has been demonstrated that the specific pillaring synthesis procedure and further addition of the Ti pillared sites greatly contributed to the wide active temperature window and enhanced the resistance to alkali and heavy metal. The higher ratio of active Fe2+ species, more active acid sites, and enhanced ammonia adsorption indicated the remarkable activity as well as K and Pb resistance. Moreover, the K and Pb poisons would promote the generation of active adsorbed NOx species on the Fe-Ti-MMT but induce the formation of stable inactive ones on that of Fe-MMT, which greatly tuned the reaction pathways and improved the reaction rate for Ti modified Fe pillared MMT catalysts. The strategy of incorporating Ti into the Fe pillared MMT catalysts strongly provides a novel inspiration for keeping excellent NH3-SCR performance in the presence of alkali/heavy metal for NOx removal.

The Influence of Ce or Mn Doping on Cu-Based Catalysts for De-NOx with NH3-SCR

In this study, the de-NOx performance of Cu-based zeolite catalysts supported on topological structure (SSZ-13, BEA, ZSM-5) and loaded with different doses of copper (from 2 to 6 wt.%) was investigated. The preparation of copper-based catalysts adopted the incipient wetness impregnation method. To analyze the physicochemical properties of the catalysts, advanced techniques like BET, XRD, NH3-TPD, H2-TPR, and DRS UV-Vis were used. The performance tests suggested the 4Cu/SSZ-13 catalyst exhibited higher low-temperature activity and wider temperature window. Furthermore, compared with Mn-Cu/SSZ-13, the Ce-Cu/SSZ-13 catalysts exhibited better de-NOx performance.

Ammonia storage/release characteristics of CeSnWBaOx/TiO2 catalyst in solving the problem of ammonia slip

The ceria-based catalyst exhibited excellent storage/release characteristics of ammonia, ensuring stable deNOx efficiency under fluctuating engineering conditions, while greatly reducing ammonia slip. In this work, characteristics of ammonia storage/release of CeSnWBaOx/TiO2 catalyst were investigated. Results showed that the catalyst exhibited much higher catalytic activity than the theoretical maximum under low NH3/NO ratios. Especially, the amount of effective ammonia release reached maximum at 250 °C with increase of excess NO. Low temperature was conducive to storage and the stable storage amount was 22.97 μmol·m−2 at 50 °C, effective release of ammonia occurred mainly at the active temperature window. Ammonia storage of the CeSnWBaOx/TiO2 catalyst was affected by the activation of active sites and thermal vibration at the same time. Ammonia storage under low temperature was mainly in physical form and at weak acid sites, while high temperature enhanced activation of ammonia, resulting in an increase of ammonia storage at 350 °C. The catalyst had both weak and strong stored-ammonia, strong stored-ammonia could be effectively released only in the induction of NO. Ammonia storage of catalyst was the key to ensure stable deNOx efficiency under fluctuating engineering condition. The characteristics are of great guiding significance for dealing with ammonia slip.

Preparation of the Coupling Co-Precipitation and Impregnation Catalyst Ag/Al₂O₃ with High Catalytic Performance in Selective Catalytic Reduction of NO with C₃H6.

This brief paper reported an Ag/Al₂O₃ catalyst of high catalytic performance in C₃H6-SCR (selective catalytic reduction with C₃H6 as the reducer), and demonstrated a new strategy for the preparation of high active Ag/Al₂O₃ catalyst by the coupling co-precipitation and impregnation method. The results show that the coupling co-precipitation and impregnation catalyst was higher active than the usual impregnated catalyst in C₃H6-SCR of NO with broad active temperature window (420-600 °C), and the highest conversions of NO achieved 91% over the coupling co-precipitation and impregnation catalyst at 500 °C. The porous structure parameter, crystal phase structure, surface acidity property and particle morphology of the Ag/Al₂O₃ catalyst were characterized by the Brunauer-Emmett-Teller (BET) method, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis spectra and temperature programmed desorption of ammonia (NH₃-TPD), respectively. Based on the characterization, it is found that the catalyst prepared by the coupling co-precipitation and impregnation method has smaller particles and better dispersion than the usual impregnated catalyst, and so the catalyst exhibited excellent catalytic activity. NH₃-TPD results illustrate that the weak and medium-strong acid sites is conducive to the reactivity of catalyst.