Supported MoO3 catalysts: preparation by the new “slurry impregnation” method and activity in hydrodesulphurization

A new preparation of supported MoO₃ is described. Slurry MoO₃/water is used instead of the solution (NH₄)₆Mo₇O₂₄. Preparation and HDS activity are illustrated for MoO₃ supported over Al₂O₃, active carbon and ZrO₂. Another application of the new principle is the preparation of high surface area MoO₃/MgO by the reaction of MgO with slurry (NH₄)₆Mo₇O₂₄/methanol. Texture of MgO that is deteriorated in aqueous solution of (NH₄)₆Mo₇O₂₄ is stable in that slurry. “Slurry impregnation” is a special case of equilibrium adsorption impregnation. It is simple and it provides monolayer dispersion of molybdena.     

Molybdenum-titanium oxide catalysts: the influence of the preparation conditions on their activity for the selective catalytic reduction of NO by NH3

MoO₃/TiO₂ catalysts of varying molybdenum content were prepared at various pHs and concentrations of the impregnating solution using the equilibrium deposition filtration (EDF) method. Moreover, a catalyst corresponding to the EDF one with the maximum Mo loading was prepared using the conventional non-dry impregnation (NDI) method. The above catalysts were characterized using X-ray powder analysis, diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy, and tested for the selective catalytic reduction of NO by NH₃ in the temperature range 250–450 °C. It was found that the application of EDF results in an improved MoO₃/TiO₂ catalyst exhibiting higher activity than the corresponding sample prepared by the conventional NDI method. The catalytic activity correlates well with the concentration of the Mo species strongly interacting with the anatase surface. The concentration of the above species is maximized when the EDF method is employed to prepare the catalysts. This is especially, so when low pH and Mo concentration of impregnating solution are used.     

Synthesis of bulk and alumina-supported γ-Mo2N catalysts by a single-step complex decomposition method

A single-step complex decomposition method for the synthesis of bulk and alumina-supported γ-Mo₂N catalysts is described. The complex precursor (HMT)₂(NH₄)₄Mo₇O₂₄·2H₂O (HMT: hexamethylenetetramine) is converted to γ-Mo₂N under a flow of Ar in a temperature range of 823–1023 K. Furthermore, decomposition of the precursor in a NH₃ flow forms γ-Mo₂N in a temperature range of 723–923 K. Compared with direct decomposition of the precursor in Ar, the reaction in NH₃ shows obvious advantages that the nitride forms at a lower temperature. In addition, alumina-supported γ-Mo₂N catalysts with different nitride loadings can be prepared from the alumina-supported complex precursor in the Ar or NH₃ flow. The resultant catalysts exhibit good dibenzothiophene HDS activities, which are similar to the γ-Mo₂N/γ-Al₂O₃ prepared by traditional TPR method. The catalyst prepared by decomposition in an Ar flow exhibits highest activity. It proves that such a single-step complex decomposition method possesses the potential to be a general route for the preparation of molybdenum nitride catalysts.     

TPD study and carbazole hydrodenitrogenation activity of nitrided molybdena–alumina

The relationship between the activity and surface molybdenum species of nitrided 12.5% MoO₃/Al₂O₃ was studied in the hydrodenitrogenation (HDN) of carbazole at 573 K and 10.1 MPa total pressure. The surface molybdenum species were determined by the desorption of nitrogen gas during TPD. The surface area of NH₃-cooled Mo/Al₂O₃ nitrided at 773 and 1173 K was decreased by 8% and 61% from 245 m² g⁻¹ of the fresh MoO₃/Al₂O₃, respectively. The NH₃-cooled Mo/Al₂O₃ catalysts had slightly higher surface area than the He-cooled catalysts. The HDN rate increased with increasing nitriding temperature in the HDN of carbazole on the nitride catalysts. The NH₃-cooled Mo/Al₂O₃ catalysts nitrided at 1173 K were the most active in carbazole HDN and the He-cooled catalyst nitrided at 773 K was the least.     

A study on the preparation of supported metal oxide catalysts using JRC-reference catalysts. I. Preparation of a molybdena–alumina catalyst. Part 2. Volume of an impregnation solution

Ten types of 13 wt% MoO₃/Al₂O₃ catalysts were prepared by a conventional impregnation or equilibrium adsorption method using a common extrudate support. These catalysts were subjected to a comprehensive characterization and catalytic reactions to find important preparation parameters in practical preparations. It was demonstrated in the present group study that the formation of crystalline MoO₃ was strongly correlated with the Mo segregation on the outer surface of the extrudate. When the amount of the impregnation solution was large (ca. 10 cm³ g-Al₂O₃⁻¹), a considerably homogeneous distribution and high dispersion of Mo oxide species were attained irrespective of the other preparation parameters. It is suggested that when a pore volume impregnation or incipient wetness technique is employed, drying processes strongly affect the dispersion and distribution of Mo oxide species. Drying at a reduced pressure is suggested to result in a segregation of Mo oxides on the outer surface of the extrudate, and accordingly a formation of crystalline MoO₃.     

MgO-supported Mo, CoMo and NiMo sulfide hydrotreating catalysts

The most common preparation of high surface area MgO (100–500 m² g⁻¹) is calcination of Mg(OH)₂ obtained either by precipitation or MgO hydration or sol–gel method. Preparation of MoO₃/MgO catalyst is complicated by the high reactivity of MgO to H₂O and MoO₃. During conventional aqueous impregnation, MgO is transformed to Mg(OH)₂, and well soluble MgMoO₄ is easily formed. Alternative methods, that do not impair the starting MgO so strongly, are non-aqueous slurry impregnation and thermal spreading of MoO₃. Mo species of MoO₃/MgO catalyst are dissolved as MgMoO₄ during deposition of Co(Ni) by conventional aqueous impregnation. This can be avoided by using non-aqueous impregnation. Co(Ni)Mo/MgO catalysts must be calcined only at low temperature because Co(Ni)O and MgO easily form a solid solution. Literature data on hydrodesulfurization (HDS) activity of MgO-supported catalysts are often contradictory and do not reproduced well. However, some results suggest that very highly active HDS sites can be obtained using this support. Co(Ni)Mo/MgO catalysts prepared by non-aqueous impregnation and calcined at low temperature exhibited strong synergism in HDS activity. Co(Ni)Mo/MgO catalysts are much less deactivated by coking than their Al₂O₃-supported counterparts. Hydrodenitrogenation (HDN) activity of Mo/MgO catalyst is similar to the activity of Mo/Al₂O₃. However, the promotion effect of Co(Ni) in HDN on Co(Ni)Mo/MgO is lower than that on Co(Ni)Mo/Al₂O₃.     

Hydrodesulfurization over supported monometallic, bimetallic and promoted carbide and nitride catalysts

The preparation of alumina-supported β-Mo₂C, MoC_1−x (x≈0.5), γ-Mo₂N, Co–Mo₂C, Ni₂Mo₃N, Co₃Mo₃N and Co₃Mo₃C catalysts is described and their hydrodesulfurization (HDS) catalytic properties are compared to conventional sulfide catalysts having similar metal loadings. Alumina-supported β-Mo₂C and γ-Mo₂N catalysts (Mo₂C/Al₂O₃ and Mo₂N/Al₂O₃, respectively) are significantly more active than sulfided MoO₃/Al₂O₃ catalysts, and X-ray diffraction, pulsed chemisorption and flow reactor studies of the Mo₂C/Al₂O₃ catalysts indicate that they exhibit strong resistance to deep sulfidation. A model is presented for the active surface of Mo₂C/Al₂O₃ and Mo₂N/Al₂O₃ catalysts in which a thin layer of sulfided Mo exposing a high density of sites forms at the surface of the alumina-supported β-Mo₂C and γ-Mo₂N particles under HDS conditions. Cobalt promoted catalysts, Co–Mo₂C/Al₂O₃, have been found to be substantially more active than conventional sulfided Co–MoO₃/Al₂O₃ catalysts, while requiring less Co to achieve optimal HDS activity than is observed for the sulfide catalysts. Alumina-supported bimetallic nitride and carbide catalysts (Ni₂Mo₃N/Al₂O₃, Co₃Mo₃N/Al₂O₃, Co₃Mo₃C/Al₂O₃), while significantly more active for thiophene HDS than unpromoted Mo nitride and carbide catalysts, are less active than conventional sulfided Ni–Mo and Co–Mo catalysts prepared from the same oxidic precursors.     

Selective catalytic reduction of NO by ammonia using mesoporous Fe-containing HZSM-5 and HZSM-12 zeolite catalysts: An option for automotive applications

Mesoporous and conventional Fe-containing ZSM-5 and ZSM-12 catalysts (0.5–8 wt% Fe) were prepared using a simple impregnation method and tested in the selective catalytic reduction (SCR) of NO with NH₃. It was found that for both Fe/HZSM-5 and Fe/HZSM-12 catalysts with similar Fe contents, the activity of the mesoporous samples in NO SCR with NH₃ is significantly higher than for conventional samples. Such a difference in the activity is probably related with the better diffusion of reactants and products in the mesopores and better dispersion of the iron particles in the mesoporous zeolite as was confirmed by SEM analysis. Moreover, the maximum activity for the mesoporous zeolites is found at higher Fe concentrations than for the conventional zeolites. This also illustrates that the mesoporous zeolites allow a better dispersion of the metal component than the conventional zeolites. Finally, the influence of different pretreatment conditions on the catalytic activity was studied and interestingly, it was found that it is possible to increase the SCR performance significantly by preactivation of the catalysts in a 1% NH₃/N₂ mixture at 500 °C for 5 h. After preactivation, the activity of mesoporous 6 wt% Fe/HZSM-5 and 6 wt% Fe/HZSM-12 catalyst is comparable with that of traditional 3 wt% V₂O₅/TiO₂ catalyst used as a reference at temperatures below 400 °C and even more active at higher temperatures.     

Evaluation of the role played by bismuth molybdates in Bi2Sn2O7–MoO3 catalysts used for partial oxidation of isobutene to methacrolein

The catalytic behaviour of multiphasic catalysts based on -bismuth pyrostannate, Bi₂Sn₂O₇, was investigated in the selective oxidation of isobutene into methacrolein. When -Bi₂Sn₂O₇ is mixed with MoO₃, strong cooperation effects on the yield and selectivity in methacrolein occur. However, XRD analyses performed on samples after test revealed the formation of a low quantity of -bismuth molybdate, -Bi₂Mo₃O₁₂, when the reaction temperature exceeded 673 K. Additional experiments were therefore carried out on the “Bi–Sn–Mo–O” catalysts in order to shed light on the role of Bi₂Mo₃O₁₂ in the synergetic effects observed in the Bi₂Sn₂O₇–MoO₃ system. The experimental results are discussed in terms of several hypotheses. First, the intrinsic activity of Bi₂Mo₃ O₁₂ is probably the simplest explanation for the synergetic effects, although experiments have shown that this phase present in a low quantity is only poorly active. Second, catalytic tests made on Bi₂Sn₂O₇–Bi₂Mo₃O₁₂ mechanical mixtures have evidenced a cooperation between these two ternary oxides, particularly when Bi₂Sn₂O₇ was the major component of the mixture. Consequently, it is likely that a synergy between Bi₂Sn₂O₇ and the in situ generated Bi₂Mo₃O₁₂ might play a role in the synergy observed in the Bi₂Sn₂O₇–MoO₃ association. Third, as bismuth pyrostannate was previously shown to behave as an oxygen donor phase with respect to WO₃, a remote control mechanism could therefore occur between Bi₂Sn₂O₇ and MoO₃, independently from the formation of -Bi₂Mo₃O₁₂.     

Effects of small MoO3 additions on the properties of nickel catalysts for the steam reforming of hydrocarbons III. Reduction of Ni-Mo/Al2O3 catalysts

Ni/Al₂O₃ catalyst modified by small amounts of Mo show unusual properties in the steam reforming of hydrocarbons. There are no data about the effect of small amounts of molybdenum on reduction of the Ni-Mo supported catalysts. The properties of these very complex systems depend on the conditions of successive preparation stages (calcination, reduction) or the process conditions.

A series of Ni/Al₂O₃ catalysts modified by Mo were prepared in order to investigate the influence of promoter amounts and preparation sequence on their properties. Temperature programmed reduction (TPR) has been employed to study the reducibility of Ni-Mo/Al₂O₃ catalysts. Catalysts were further characterized by BET area, H₂ chemisorption and X-ray diffraction measurements.

The TPR curves of Ni-Mo/Al₂O₃ catalysts are very complex. Mo addition leads to the decrease of catalysts reducibility. However, complete reduction of NiO and MoO₃ can be achieved at 800 °C. The reduction course depends on the sequence of nickel and molybdenum addition into the support. Precise measurements of Ni peaks positions in the XRD pattern of Ni/Al₂O₃ and Ni-Mo/Al₂O₃ samples show the possibility of Ni-Mo solid solution formation.     

High-throughput preparation and testing of MoNbSbV mixed oxide catalysts for direct oxidation of propane to acrylic and acetic acids

An automated robotic method using a solution at pH=2 containing four precursor salts dissolved has been developed and validated for high-throughput preparation of Mo, Nb, Sb and V mixed metal oxide solids, which are known to be selective for propane oxidation to acrylic (AA) and acetic (AcA) acids. Spherical shaped silica beads of exceptionally narrow size distribution were synthesised using oil drop technique from a Brace™ instrument. Automated impregnation of the beads by the previous solution has been developed and validated. Catalytic studies were performed using a conventional micro-reactor system with an Ultra-Fast™ GC analysis (<2 min against >30 min). After calcination of the samples under either N₂ or air at 873 K, a mixture of phases was obtained, such as VSbO₄, Mo_xM_1−xO_2.8 (M=V and/or Nb), Sb₄₍₂₎Mo₁₀O₃₁, and other minor phases, such as MoO₃ if activated in air. Mixed oxide samples calcined under N₂ gave better catalytic activity and selectivity to AA/AcA compared to those calcined under air. Measures of catalytic performance of 16 supposedly identical materials fell within a ±5% range of the median values, showing that our experimental set-up is relevant to combinatorial studies. By preparing 15 samples of different chemical composition, optimum catalytic performance was found to correspond to Mo_0.55 Nb_0.09 Sb_0.18V_0.18 mixed oxide calcined at 773 K under N₂, containing a mixture of phases, in particular Mo_xM_1−xO_2.8 and Sb₂Mo₁₀O₃₁, similarly to the M1 and M2 phases observed for MoNbTeV mixed oxide catalysts.     

Catalytic selective reduction of NO with propylene over Cu-Al2O3 catalysts: influence of catalyst preparation method

NO reduction to N₂ by C₃H₆ was investigated and compared over Cu-Al₂O₃ catalysts prepared by four different methods, namely, the conventional impregnation, co-precipitation, evaporation of a mixed aqueous solution, and xerogel methods. It was found that the catalyst preparation method as well as the Cu content exerts a significant influence on catalyst activity. For the catalysts prepared by the first three preparation methods, with the increase of Cu content from 5 to 15 wt%, the maximum NO reduction conversion decreased slightly, but the temperature for the maximum NO reduction also decreased. For the xerogel Cu-Al₂O₃, there was a significant decrease in NO reduction conversion with the increase of Cu content from 5 to 10 wt%. In the absence of water vapour, the Cu-Al₂O₃ catalyst prepared by the impregnation method exhibited the highest activity toward NO reduction. The purity of alumina support was found to be a crucial factor to the activity of the Cu-Al₂O₃ catalyst prepared by impregnation. In the presence of water vapour, a substantial decrease in NO conversion was observed for the Cu-Al₂O₃ catalysts prepared by the first three methods, especially for the impregnated Cu-Al₂O₃ catalyst. In contrast, the presence of water vapour showed only a minor influence on the xerogel 5 wt% Cu-Al₂O₃ and it showed the highest activity for NO reduction in the presence of 20% water vapour. The xerogel 5 wt% Cu-Al₂O₃ catalyst was also found to be less affected by a 5 wt% sulfate deposition than the Cu-Al₂O₃ catalysts prepared by other methods.     

Selective oxidative dehydrogenation of propane over surface molybdenum-enriched MgMoO4 catalyst

Drastic activity increases were observed by the treatments of the magnesium-rich MgMo_0.99O_y catalysts, which are poorly active for the oxidative dehydrogenation of propane, with inorganic or organic acid to remove excess magnesium on the surface. MoO₃ loading on magnesium-rich MgMo_0.99O_y catalysts also resulted in drastic activity increases. The activity increases followed non-effective loadings of MoO₃ in the range 0–2 wt%, because it is necessary to neutralize the surface magnesium with MoO₃ before the formation of molybdenum-rich surface. The pH of the aqueous (NH₄)₆Mo₇O₂₄ solution for the MoO₃ loading apparently influenced the activity. Under the acidic conditions the MoO₃ loading resulted in the drastic activity increase but under the basic conditions the effect of the MoO₃ loading was poor, suggesting that a cluster-type MoO₃ on MgMoO₄ surface is responsible for the activity of propane oxidative dehydrogenation.     

A study on the preparation of supported metal oxide catalysts using JRC-reference catalysts. I. Preparation of a molybdena–alumina catalyst. Part 4. Preparation parameters and impact index

The effects of the volume and pH of the impregnation solution and of the calcination conditions were examined on the physicochemical and catalytic properties of a 13 wt% MoO₃/Al₂O₃ extrudate catalyst. The Al₂O₃ support and drying procedures (static conditions without flowing air) were fixed in the preparations. In the present series of catalysts, the amount of crystalline MoO₃ was marginally small. It was found that the dispersion of Mo oxide species increased as the volume of the impregnation solution increased, gradually approaching a maximum value. The increase in pH (2–8) of the impregnation solution was found to reduce the dispersion of Mo oxide species. The Mo dispersion increased slightly for the impregnation catalysts as the calcination temperature increased (673–873 K), whereas it decreased for the equilibrium adsorption catalysts. The effects of the calcination atmosphere (with or without flowing air, or with flowing humid air) were very small on the dispersion of Mo oxide species under the present preparation conditions. On the other hand, the methanol oxidation activity of MoO₃/Al₂O₃ was sensitive to the preparation parameters examined here. It was demonstrated by means of EPMA and XPS that a considerable migration of Mo took place during the calcination.

In the present study on the preparation of a 13 wt% MoO₃/Al₂O₃ catalyst, an impact index is proposed to measure the magnitude of the effects of the respective parameter(s) on the physicochemical and catalytic properties. With the Mo dispersion, the effects of the preparation parameter decreased in the order, surface area of the support >> drying process > volume of the impregnation solution > pH, calcination temperature and atmosphere. The size of the impact index for the dispersion of Mo sulfide species is 70–75% of that for the Mo oxide species. The HDS activity of the catalyst was less affected by the preparation parameters than the Mo sulfide dispersion. The preparation parameters affected the segregation of Mo on the outer surface of extrudates in a decreasing order: drying process > volume of the impregnation solution > pH, calcination conditions. It was found that the oxidation of methanol was affected most intensely by the drying procedures. The volume of the impregnation solution, calcination conditions and pH of the impregnation solution also strongly affected the oxidation activity. The impact index suggests that the sensitivity to the preparation variables of the physicochemical and catalytic properties of MoO₃/Al₂O₃ decreases in the order, methanol oxidation activity > surface Mo segregation > Mo oxide dispersion > Mo sulfide dispersion > HDS activity.     

The role of molybdenum in Mo-doped V–Mg–O catalysts during the oxidative dehydrogenation of n-butane

A detailed study on the influence of the addition of molybdenum ions on the catalytic behaviour of a selective vanadium–magnesium mixed oxide catalyst in the oxidation of n-butane has been performed. The catalysts have been prepared by impregnation of a calcined V–Mg–O mixed oxides (23.8 wt% of V₂O₅) with an aqueous solution of ammonium heptamolybdate, and then calcined, and further characterised by several physico-chemical techniques, i.e. S_BET, XRD, FTIR, FT-Raman, XPS, H₂-TPR. MgMoO₄, in addition to Mg₃V₂O₈ and MgO, have been detected in all the Mo-doped samples. The incorporation of molybdenum modifies not only the number of V⁵⁺-species on the catalyst surface and the reducibility of selective sites but also the catalytic performance of V–Mg–O catalysts. The incorporation of MoO₃ favours a selectivity and a yield to oxydehydrogenation products (especially butadiene) higher than undoped sample. In this way, the best catalyst was obtained with a Mo-loading of 17.3 wt% of MoO₃ and a bulk Mo/V atomic ratio of 0.6. From the comparison between the catalytic properties and the catalyst characterisation of undoped and Mo-doped V–Mg–O catalysts, the nature of selective sites in the oxidative dehydrogenation of n-butane is also discussed.     

液相原位还原法制备钯基催化剂

采用液相原位还原法制备Pd/α-Al2O3催化剂,并应用于CO氧化偶联合成草酸二甲酯反应。对比实验发现,甲醛液相原位还原法制得的Pd基催化剂具有优异的催化活性,当Pd负载质量分数低至0.1%时,催化剂仍表现出较高的活性和稳定性。采用XRD和BET等对催化剂及载体进行表征,结果表明,催化剂活性与载体的比表面积、孔容和孔径没有必然联系。通过TEM发现,0.1%-Pd/α-Al2O3催化剂中的主要活性组分Pd具有较小的颗粒和较高的分散性,通过HRTEM发现,液相原位还原法制备的催化剂能够有效暴露出Pd(111)晶面。     

Effects of microwaves on selective oxidation of toluene to benzoic acid over a V2O5/TiO2 system

Two series of catalysts, V₂O₅/TiO₂ and modified V₂O₅/TiO₂, were prepared with a conventional impregnation method. They were tested in the selective oxidation of toluene to benzoic acid under microwave irradiation. The reaction conditions were optimized over V₂O₅/TiO₂. It was found that in the microwave catalytic process the optimum reactor bed temperature of the titled reaction decreases to 500 K (600 K in the conventional process). The modification of V₂O₅/TiO₂ with MoO₃, WO₃, Nb₂O₅ or Ta₂O₅, which has no negative influence on the reaction in the conventional catalytic process, can greatly promote the catalytic activities in the microwave process, leading to a high yield of benzoic acid (41%). The effects of microwave electromagnetic field on the catalysts are discussed.     

The structure analysis of MoOx/TiO2(110) by polarization-dependent total-reflection fluorescence X-ray absorption fine structure

The surface structure analysis of a model catalyst MoO_x/TiO₂(110) was for the first time performed by polarization-dependent total-reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) in three different directions of the crystal surface. Two samples of MoO_x/TiO₂(110) were prepared by an impregnation of (NH₄)₆Mo₇O₂₄·4H₂O using ultra high purity water and normal distilled water. The PTRF-XAFS analysis revealed that anisotropic Mo dimer species was preferentially formed on the TiO₂(110) surface, with Mo–Mo bond (0.335 nm) parallel to the direction when the ultra high purity water was used as the solvent. On the other hand, the Mo oxide on the surface prepared using normal distilled water had a symmetric tetrahedral structure (MoO₄) with Mo–O of 0.176 nm, which was due to the coexistence of alkaline metals at the surface.     

WO3–TiO2 monolithic catalysts for high temperature SCR of NO by NH3: Influence of preparation method on structural and physico-chemical properties, activity and durability

The WO₃–TiO₂ catalysts with different WO₃ loadings prepared by the coprecipitation method were investigated in comparison with those prepared by the conventional impregnation method for the activity and durability in the high temperature SCR of NO by NH₃ and the structural and physico-chemical properties which were characterized by BET and XRD measurements, IR, Raman and XPS spectroscopies. The catalyst prepared by coprecipitation, as compared with that prepared by impregnation, was found to exhibit a higher SCR activity at high temperatures and also to possess a larger surface area, higher Brønsted acidity and larger monolayer capacity of the support with WO₃. Increasing the WO₃ loading of the catalysts enhances the SCR activity and simultaneously increases the Brønsted acidity. The observed improvement of SCR activity for the catalyst prepared by coprecipitation is mainly attributed to the higher Brønsted acidity and the presence of the more highly dispersed WO₃ species which is suggested by the larger monolayer capacity of ca. 13 μmol(W)/m² and no crystalline WO₃ on TiO₂ detected with XRD at the high WO₃ loading up to 40 wt.%. The catalyst with 20 wt.% WO₃, as compared with that prepared by impregnation, was found to exhibit a better thermal durability at high temperatures from 550 to 600 °C. The better durability is attributed to that the reduction of the surface area and the formation and subsequent growth of crystalline WO₃ upon aging are more remarkably inhibited.     

Catalytic performance of a novel ceramic-supported vanadium oxide catalyst for NO reduction with NH3

A novel TiO₂/Al₂O₃/cordierite honeycomb-supported V₂O₅–MoO₃–WO₃ monolithic catalyst was studied for the selective reduction of NO with NH₃. The effects of reaction temperature, space velocity, NH₃/NO ratio and oxygen content on SCR activity were evaluated. Two other V₂O₅–MoO₃–WO₃ monolithic catalysts supported on Al₂O₃/cordierite honeycomb or TiO₂/cordierite honeycomb support, two types of pellet catalysts supported on TiO₂/Al₂O₃ or Al₂O₃, as well as three types of pellet catalysts V₂O₅–MoO₃–WO₃–Al₂O₃ and V₂O₅–MoO₃–WO₃–TiO₂ were tested for comparison. The experiment results show that this catalyst has a higher catalytic activity for SCR with comparison to others. The results of characterization show, the preparation method of this catalyst can give rise to a higher BET surface area and pore volume, which is strongly related with the highly active performance of this catalyst. At the same time, the function of the combined carrier of TiO₂/Al₂O₃ cannot be excluded.