Influence of the V2O5 Loading on the Structure and Activity of V2O5/TiO2 SCR Catalysts for Vehicle Application

In this paper the effect of the vanadium oxide loading on the surface vanadia structure and the activity as well as selectivity in the catalytic reduction of NO with NH₃ was studied for a V₂O₅/TiO₂ model system. A series of TiO₂ (WO _x stabilized anatase) supported vanadia catalysts with varying loadings were characterized by laser Raman spectroscopy, ⁵¹V MAS-NMR, V K XANES. To determine the acidic properties, DRIFTS measurements were done with pyridine adsorbed on the samples. The measurements indicate that with increasing active phase loading square pyramidal coordinated surface vanadia species are replaced by an amorphous highly dispersed vanadium oxide phase with a coordination like V₂O₅. In addition, the ratio of Brønsted to Lewis acid sites is shifted from a comparatively low to an equal level at high loadings. This structural change is accompanied by a clearly improved catalytic activity and selectivity.     

Ru-Promoted CrO x /Al2O3 Catalyst for the Low-Temperature Oxidative Decomposition of Trichloroethylene in Air

A series of Ru-promoted CrO _x /Al₂O₃ as catalysts for the low-temperature oxidative decomposition of trichloroethylene (TCE) were characterized and evaluated in comparison with an unpromoted CrO _x /Al₂O₃ catalyst. Catalyst characterization was conducted by surface area measurement, X-ray diffraction and X-ray photoelectron spectroscopy. Catalyst performance in the TCE decomposition reaction was evaluated with respect to the initial catalytic activity, the rate of catalyst deactivation, and the product concentrations of CO and Cl₂ under dry or wet air conditions. The presence of a small amount of Ru, as much as 0.4 wt% in a CrO _x /Al₂O₃ catalyst, brought about several beneficial effects on the catalytic reaction performance. As compared with the unpromoted CrO _x /Al₂O₃, this Ru-promoted CrO _x /Al₂O₃ catalyst showed enhanced catalytic activity (249 versus 264 °C in terms of temperature at which 50% of TCE conversion occurred), a reduced concentration of CO (180 versus 325 ppm) in the product, and a decreased propensity to deactivation. Performance improvements of the Ru-promoted CrO _x /Al₂O₃ catalyst were thought to originate from its enhanced oxidation activity due to the coexisting highly-dispersed Ru oxides rendering less active Cr(III) to more active Cr(VI), and facilitating the process of supplying activated oxygen for the reaction system.     

Influence of Al2O3 support on the activity of Ag/Al2O3 catalysts for SCR of NO with decane

The role of the Al₂O₃ support on the activity of supported Ag catalyst towards the selective catalytic reduction (SCR) of NO with decane is elucidated. A series of Ag/Al₂O₃ catalysts were prepared by impregnation method and characterized by N₂ pore size distribution, XRD, UV–Vis, in-situ FT-IR and acidity measurement by NH₃ and pyridine adsorption. The catalytic activity differences of Ag/Al₂O₃ are correlated with different properties of Al₂O₃ supports and the active Ag species formed. 4wt% Ag supported on sol-gel prepared Al₂O₃ (Ag/Al₂O₃ (SG), showed higher NO _x conversion (65% at 400 °C), compared with the respective catalysts made from commercial Al₂O₃ (Ag/Al₂O₃ (GB), Ag/Al₂O₃ (ALO), (∼26 and 7% at 400 °C). The higher surface area, acidity and pore size distribution in sol–gel prepared Al₂O₃ (SG) results in higher NO and hydrocarbon conversion. Based on the UV–vis characterization, the activity of NO reduction is correlated to the presence of Ag_n^δ+ clusters and acidity of Al₂O₃ support was found to be one of the important parameter in promoting the formation and stabilization of Ag_n^δ+ clusters. Furthermore from pyridine adsorption results, presence of more number of Bronsted acid sites in Ag/Al₂O₃ (SG) is confirmed, which could also contribute to low temperature hydrocarbon activation and improve NO conversion. In situ FT-IR measurements revealed the higher rate of –CN and –NCO intermediate species formation over 4wt% Ag/Al₂O₃ (SG). We conclude that the physico–chemical properties of Al₂O₃ play a crucial role in NO _x conversion over Ag/Al₂O₃ catalysts. Thus, the activity of the Ag/Al₂O₃ catalyst can be tailored by using a proper type of Al₂O₃ support.     

Novel Sn–Ce/Al2O3 Catalyst for the Selective Catalytic Reduction of NOx Under Lean Conditions

Effect of additives, Ce and Mn, on the catalytic performance of Sn/Al₂O₃ catalyst prepared by sol–gel method for the selective reduction of NO_x with propene under lean conditions was studied. Sn–Ce/Al₂O₃ catalysts exhibited higher activity than Sn/Al₂O₃ catalyst and the optimum Ce loading is 0.5–1%. The promoting effect of Ce is to enhance the oxidation of NO to NO₂ and facilitate the activation of propene, both of which are important steps for the NO_x reduction. The presence of oxygen contributes to the oxidation of NO and shows a promoting effect.     

A Flower-like In2O3 Catalyst Derived via Metal–Organic Frameworks for Photocatalytic Applications

The most pressing concerns in environmental remediation are the design and development of catalysts with benign, low-cost, and efficient photocatalytic activity. The present study effectively generated a flower-like indium oxide (In₂O₃-MF) catalyst employing a convenient MOF-based solvothermal self-assembly technique. The In₂O₃-MF photocatalyst exhibits a flower-like structure, according to morphology and structural analysis. The enhanced photocatalytic activity of the In₂O₃-MF catalyst for 4-nitrophenol (4-NP) and methylene blue (MB) is likely due to its unique 3D structure, which includes a large surface area (486.95 m² g⁻¹), a wide spectrum response, and the prevention of electron–hole recombination compared to In₂O₃-MR (indium oxide-micro rod) and In₂O₃-MD (indium oxide-micro disc). In the presence of NaBH₄ and visible light, the catalytic performances of the In₂O₃-MF, In₂O₃-MR, and In₂O₃-MD catalysts for the reduction of 4-NP and MB degradation were investigated. Using In₂O₃-MF as a catalyst, we were able to achieve a 99.32 percent reduction of 4-NP in 20 min and 99.2 percent degradation of MB in 3 min. Interestingly, the conversion rates of catalytic 4-NP and MB were still larger than 95 and 96 percent after five consecutive cycles of catalytic tests, suggesting that the In₂O₃-MF catalyst has outstanding catalytic performance and a high reutilization rate.     

Influence of Preparation Methods of In2O3/Al2O3 Catalyst on Selective Catalytic Reduction of NO by Propene in the Presence of Oxygen

Selective catalytic reduction of NO with propene was investigated over In₂O₃/Al₂O₃ catalysts prepared by three methods, namely, a single sol-gel (SG), impregnation (IM), and co-precipitation method (CP). The catalysts were characterized by means of BET, XRD, XPS, and TPD. The maximum NO conversion over In₂O₃/Al₂ O₃ prepared by sol-gel method was 95% at 400 °C in the absence of H₂O, and the activity decreased slightly in the presence of H₂O, and it was still 76% even in the presence of H₂O and SO₂. Although the retarding effect of SO₂ on the activity was observed for the three catalysts, In₂O₃/Al₂O₃ (SG) showed relatively high activity. It is found that the high surface area and low average pore diameter are important to the catalytic activity, and the strong interaction between indium and alumina for In₂O₃/Al₂O₃ catalyst prepared by sol-gel method may be the reason of high activity for NO reduction. The reaction and surface studies showed that NO₃⁻ and partially oxidized hydrocarbons (RCOO⁻ species) are mainly intermediates, and the oxidation C₃H₆ to RCOO⁻ species maybe the key reaction process in the SCR of NO with C₃H₆.     

Catalytic Conversions of Polychlorinated Benzenes and Dioxins with Low-chlorine Using V2O5/TiO2

Chlorinated benzene, especially 1,2-dichlorobenzene (1,2-DCB), has been widely used as one of surrogate compounds of dioxin to find the noble methods to control dioxin. However, the relationship between the catalytic activity of dioxin surrogate compound and dioxin has not been understood quite well. In this work, we used a vanadium based catalyst (V₂O₅/TiO₂) to compare catalytic activity of chlorinated benzenes and dibenzo-p-dioxins with low-chlorine content using the lab-scale system. We investigated the catalytic conversions of low-chlorinated dioxins, [2-monochlorodibenzo-p-dioxin (2-MCDD), 2,3-dichlorodibenzo-p-dioxin (2,3-DCDD)] and polychlorinated benzenes [1,2-DCB, 1,2,3,4-tetrachlorobenzene (1,2,3,4-TeCB), pentachlorobenzene (PeCB), hexachlorobenzene (HCB)] using a V₂O₅/TiO₂ catalyst to understand quantitative relationship between dioxin and benzene with the chlorination level. The catalytic decomposition of chlorinated aromatic compounds was following 1,2-DCB > 1,2,3,4-TeCB > 2-MCDD > PeCB ≥ 2,3-DCDD > HCB. It might be more reasonable that PeCB or HCB should be used as the dioxin surrogate compound rather than 1,2-DCB. Also, we investigated the effect of both O₂ content and space velocity (SV) on the catalytic decomposition of 1,2-DCB in the presence of V₂O₅/TiO₂ catalyst because these factors should be considered significantly in combustion facilities to control various pollutants. The decomposition of 1,2-DCB shows dependency on the SV while the effect of oxygen content on the catalytic decomposition is negligible in the range of 5–20%.     

Ambient temperature oxidation of carbon monoxide using a Cu2Ag2O3 catalyst

The mixed copper–silver oxide, Cu₂Ag₂O₃, has been prepared by co-precipitation and tested for ambient temperature carbon monoxide oxidation. The catalyst demonstrated appreciable low temperature oxidation activity and the catalyst aged for 4 h was the most active. Carbon monoxide conversion increased with time-on-stream, reaching steady state after ca. 1000 min. Acomparison of the catalytic activity has been made with a representative sample of a high activity hopcalite, mixed copper/manganese oxide catalyst. On the basis of CO oxidation rate data corrected for the effect of catalyst surface area the Cu₂Ag₂O₃, aged for 4 h was at least as active as the hopcalite.     

Effect of Pt Incorporation into Ni/ZrO2–SO 4 = /Al2O3 Catalyst for n-Butane Isomerization

Three Ni/ZrO₂–SO₄⁼/Al₂O₃ catalysts with different concentrations of platinum (0.2, 0.3 and 0.4 wt%) were prepare and tested for n-butane isomerization reaction at 338 K, in absence and in presence of hydrogen. The results shown that, at low temperature, platinum contributes to the olefin or butyl ion formation and the reaction follows a bimolecular pathway. However, when the reaction occurs in the presence of hydrogen, the formation of butyl ions is inhibited. The main feature of platinum addition is the stabilization of the catalytic activity, which is indicated by the slow deactivation constants compared to that of the unpromoted catalyst.     

Preparation and Characterization of Copper Catalysts Supported on Mesoporous Al2O3 Nanofibers for N2O Reduction to N2

The gas-phase hydrogenation of benzene to cyclohexane over Ce_{1 - x} Pt _x O_{2 -} (x = 0.01, 0.02) catalyst was investigated in the temperature range 80-200 °C. A 42% conversion of benzene to cyclohexane with 100% specificity was observed at 100 °C over Ce_0.98Pt_0.02O_{2 -} with a catalyst residence time of 1.22 × 10⁴ g s/mol of benzene. The activity of the catalyst was compared with those of Pt metal, combustion-synthesized Pt/-Al₂O₃ and Pt/-Al₂O₃. The turnover frequency value of Ce_0.98Pt_0.02O_{2 -} is 0.292, which is an order of magnitude higher than those of the other Pt catalysts investigated. The kinetics of reaction and the deactivation behavior of the catalyst were studied and a regeneration methodology was suggested. The deactivation kinetics and structural evidence from XRD, XPS, TGA and H₂ uptake studies suggest that the oxidized Pt in Ce_0.98Pt_0.02O_{2 -} is responsible for the high catalytic activity towards benzene hydrogenation.     

Structure Characteristics and NO Selective Catalytic Reduction Property of Sn x Zr1-x O2 Solid Solution Catalysts

Novel catalysts, Sn_xZr_1-xO₂ solid solutions, for NO selective catalytic reduction:NO SCR) are reported. They have much higher activity and selectivity than SnO₂ and ZrO₂. Sn⁴⁺ is the main reductive sites as proved by TPR. The dilution of Sn sites by the coexisting Zr causes a suppression of propene combustion and consequently promoted the selective reduction of NO. The rutile structure might be beneficial to NO SCR.     

Studies on oxidative coupling of methane using Sm2O3-based catalysts

The effects of Mn/Na₂WO₄, Li, and CaO loading on the monoclinic Sm₂O₃ catalyst were investigated for the oxidative coupling of methane using O₂ or N₂O as an oxidant. The catalysts were prepared by wet impregnation method and characterized by XRD, BET, CO₂-TPD, and XPS analysis. Impregnation of Mn/Na₂WO₄ on monoclinic Sm₂O₃ resulted in the formation of Sm_2?xMn_xO₃ phase, decreasing the catalytic performance. Li impregnation increased the C₂ selectivity but decreased the catalytic activity. The SmLiO₂ formation increased the catalytic activity and selectivity. High amounts of CaO impregnation increased the C₂ selectivity of monoclinic Sm₂O₃ without a loss in catalytic activity. 6Li/m-Sm₂O₃ were found unstable due to the Li loss from the catalyst. The 15CaO/m-Sm₂O₃ was quite stable and showed 8.2% ethylene yield with N₂O use, much higher than that was obtained with the well-known 2Mn/5Na₂WO₄/SiO₂ and 4Li/MgO catalysts. N₂O was more selective than O₂ as an oxidant and enhanced ethylene formation.     

Decomposition and oxidation of CH3 13CH2OH on A12O3, Pd/Al2O3, and PdO/Al2O3 catalysts

Temperature-programmed desorption (TPD) and oxidation (TPO) were used to investigate the decomposition and oxidation of ethanol on Al₂O₃, Pd/Al₂O₃, and PdO/Al₂O₃. Ethyl--¹³C alcohol (CH₃ ¹³CH₂OH) was adsorbed on the catalysts so that reaction pathways of the two carbons could be distinguished. Alumina was mainly a dehydration catalyst, but dehydrogenation was also observed and some carbon remained on the surface. In the presence of O₂, A1₂O₃ oxidized the decomposition products and the-carbon was oxidized faster. Ethanol, which was adsorbed on A1₂O₃, decomposed much faster on Pd/A1₂O₃ by diffusing to Pd and undergoing CO elimination to form CH₄,¹³CO, H₂, and surface carbon. On PdO/A1₂O₃, the decomposition was slower than on Pd/A1₂O₃ until lattice oxygen was extracted above 450 K; the decomposition products were oxidized by lattice oxygen. In the presence of gas phase O₂, Pd/Al₂O₃ was an active oxidation catalyst at low temperature, but lattice oxygen had to be extracted from PdO/A1₂O₃ before it had significant oxidation activity.     

Stable carbon dioxide reforming of methane over modified Ni/Al2O3 catalysts

CO₂ reforming of methane was studied over modified Ni/Al₂O₃ catalysts. The metal modifiers were Co, Cu, Zr, Mn, Mo, Ti, Ag and Sn. Relative to unmodified Ni/Al₂O₃, catalysts modified with Co, Cu and Zr showed slightly improved activity, while other promoters reduced the activity of CO₂ reforming. Mn-promoted catalyst showed a remarkable reduction in coke deposition, while entailing only a small reduction in catalytic activity compared to unmodified catalyst. The catalysts prepared at high calcination temperatures showed higher activity than those prepared at low calcination temperature. The Mn-promoted catalyst showed very low coke deposition even in the absence of diluent gas and the activity changed only slightly during 100 h operation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Catalytic Ozonation of Oxalic Acid in the Presence of Fe2O3-Loaded Activated Carbon

ABSTRACT

The activity and optimum condition of metal-loaded activated carbon catalyst (Me/AC) for oxalic acid (OA) ozonation were evaluated. Results showed that Fe-loaded activated carbon (Fe/AC) showed better activity in five kinds of Me/AC catalysts prepared by a dipping method. Fe catalyst, crystallizing as γ-Fe₂O₃, dispersed well on AC surface. Fe₂O₃/AC, with 1.12% Fe weight ratio and 450°C calcination temperature and showed better activity for OA ozonation. 89.2% of OA was removed in the Fe₂O₃/AC/O₃ process, which was higher than those in AC/O₃ (79.6%) and O₃ (3.2%) processes. The calcination process helped to promote adsorption capability and catalytic activity of AC. In addition, Surface hydroxyl groups played a key role in Fe₂O₃/AC’s catalytic activity. Acidic condition was more favorable for OA removal in the Fe₂O₃/AC/O₃ process. A hydroxyl radical (?OH) oxidation mechanism was proven in Fe₂O₃/AC/O₃. The catalytic activity of Fe₂O₃/AC remained satisfactory after several cycles, indicating that Fe₂O₃/AC had a good reusability property.     

Catalytic deNO x properties of novel vanadium oxide based open-framework materials

The deNO _x catalytic properties of a new class of open-framework structure materials, Li₆[Mn₃(H₂O)₁₂V₁₈O₄₂(XO₄)] · 24H₂O (X = V, S) (1), [Fe₃(H₂O)₁₂ V₁₈O₄₂(XO₄)] · 24H₂O (X = V, S) (2), [Co₃(H₂O)₁₂V₁₈O₄₂(XO₄)] · 24H₂O (X = V, S) (3), and Li₆[Ni ₃ ^II (H₂O)₁₂V ₁₆ ^VI V ₂ ^V O₄₂(SO₄)] · 24H₂O (4), have been studied. The crystal structures of these novel systems consist of three-dimensional arrays of vanadium oxide clusters {V₁₈O₄₂(XO₄)} , as building block units, interlinked by {–O–M–O–} (M = Mn, 1; M = Fe, 2; M = Co, 3; M = Ni, 4) bridges. Their open-framework structures contain cavities, similar to those observed in conventional zeolites, which are occupied by exchangeable cations and/or readily removable water of hydration. The catalysts derived from these materials were tested for the selective catalytic reduction (SCR) of nitrogen oxides {NO _x } into N₂ using a hydrocarbon, propylene, as the reducing agent. The catalysts were ineffective under lean burn conditions. However, the new catalysts, especially the one derived from the cobalt derivative (3), showed intriguing deNO _x activity under rich conditions. They remove up to ~ 99% of the toxic NO _x emissions in 1.5% O₂ with 100% selectivity to N₂. The active phase of the catalysts exhibit good stability, can be readily regenerated, and are selective to the desired product-N₂. The catalytic reactions occur at moderately low temperatures (400–500 °C). The catalysts were characterized by FT-IR, temperature programmed reactions (TPR and TPO), SEM, BET surface area measurements, elemental analysis, and X-ray diffraction (XRD). Additional advanced techniques were used to further characterize the catalyst phases that showed most promising deNO _x activity and increased tolerance to oxygen.     

Synthesis and Catalytic Properties of the Electrochemical NO x Reduction System

Catalytic and electrical properties of an electrochemical NO_x reduction system were investigated. This system had a laminated structure composed of BaCo(Al,Ga)₁₁O₁₉-based catalyst layer on a Pt/YSZ/Pt sheet. The stacked catalyst system can directly reduce more than 65% of NO_x to N₂ under an external bias above 2.5 V at 650 °C. In this system, oxygen existing around the catalyst layer was removed by O²⁻ transportation through the YSZ layer.     

The role of nickel in pyridine hydrodenitrogenation over NiMo/Al2O3

Al₂O₃ supported Mo, Ni, and NiMo/Al₂O₃ catalysts with various Ni contents were prepared to investigate the role of Ni as a promoter in a NiMo bimetallic catalyst system. The hydrodenitrogenation (HDN) reaction of pyridine as a catalytic probe was conducted over these catalysts under the same reaction conditions and the catalysts were characterized using BET surface area measurement, infrared spectroscopy, temperature programmed reduction, DRS and ESR. According to the results of reaction experiments, the NiMo/Al₂O₃ catalyst showed higher activity than Mo/Al₂O₃ catalyst in the HDN reaction and particularly the one with atomic ratio [Ni/(Ni+Mo)]=0.3 showed the best activity for the HDN of pyridine. The findings of this study lead us to suggest that the enhancement in the HDN activity with nickel addition could be attributed to the improvement in the reducibility of molybdenum and the formation of Ni-Mo-O phase.     

Catalytic reduction of no over perovskite-type catalysts

In the present work, we have investigated the reduction of NO by propane over perovskite-type oxides prepared by malic acid method. The catalysts were modified to enhance the activity by substitution of metal into A or B site of perovskite oxides. In addition, the reaction conditions, such as temperature, O₂ concentration, and space velocity have been varied to understand their effects on the catalytic performance. In the LaCoO₃ type catalyst, the partial substitution of Ba and Sr into A site enhanced the catalytic activity in the reduction of NO. For the La_0.6Ba (Sr)_o.4 Co_1−x Fe_xO₃ (x=0-1.0) catalyst, the partial substitution of Fe into B site enhanced the conversion of NO, but excess amount of Fe decreased the conversion of NO. The surface area and catalytic activity of perovskite catalysts prepared by malic acid method showed higher values than those of solid reaction method. The conversion of NO increased with increasing O₂ concentration and contact time. The introduction of water into reactant feed decreased the catalytic activity but the deactivation was shown to be reversible over La_0.6Ba_0.4Co_1−x ,Fe_xO₃ catalyst.     

Degradation Effect and Mechanism of Dinitrotoluene Wastewater by Magnetic Nano-Fe3O4/H2O2 Fenton-like

The characteristics and influencing factors for dinitrotoluene degradation by nano-Fe₃O₄-H₂O₂ were studied, and the nano-scale Fe₃O₄ catalyst was prepared by the coprecipitation method, with dinitrotoluene wastewater as the degradation object. The results showed that the catalytic reaction system within the pH value range of 1 to 9 could effectively degrade dinitrotoluene, and the optimal pH value was 3; with the increase of catalyst dosage, the degradation efficiency and the catalytic reaction rate of dinitrotoluene grew as well. The optimal catalyst dosage was 1.0 g/L when the H₂O₂ dosage was within the range of 0 to 0.8 mL/L; the degradation efficiency and reaction rate grew with the increase of H₂O₂ dosage. With further increase of H₂O₂ dosage, degradation efficiency and reaction rate decreased; under the best conditions with the H₂O₂ dosage of 0.8 mL/L, the catalyst concentration of 1 g/L and the pH value of 3 at room temperature (25 °C), the degradation rate of the 100-mg/L dinitrotoluene in 120 min reached 97.6%. Through the use of the probe compounds n-butyl alcohol and benzoquinone, it was proved that the oxidation activity species in the nano-Fe₃O₄-H₂O₂ catalytic system were mainly hydroxyl radical (?OH) and superoxide radicals (HO2 ?), based on which, the reaction mechanism was hypothesized.