The influence of precursors on Rh/SBA-15 catalysts for N2O decomposition

Series of Rh/SBA-15 catalysts were prepared by impregnation and grafting method applying different Rh precursors. The catalytic behaviors of N₂O decomposition over these catalysts were tested in an automated eight flow reactor system. The catalysts were characterized by X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), N₂ adsorption/desorption, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques. The results showed that the dispersion of Rh species on the catalysts is closely related to the molecular size and the hydrophobic property of the precursors comparing to the hydrophilic support, better dispersion results were found in catalysts by impregnation of smaller precursors, while by grafting better dispersion resulted from big precursor. On the other hand, the activities of the catalysts match well with the Rh dispersion status. Rh/SBA-15-CDCR starting from [(CO)₂RhCl]₂ showed good dispersion and gave the best N₂O decomposition activity.     

Synthesis and characterization of CuO/TiO2 catalysts for low-temperature CO oxidation

In this paper, the CuO/TiO₂ catalysts prepared by the deposition–precipitation (DP) method were extensively investigated for CO oxidation reaction. The structural characters of the CuO/TiO₂ catalysts were comparatively investigated by TG-DTA, XRD, and XPS measurements. It was shown that the catalytic behavior of CuO/TiO₂ catalysts greatly depended on the TiO₂-support calcination temperature, the CuO loading amount and the CuO/TiO₂ catalysts calcination temperature. CuO supported on the anatase phase of TiO₂-support calcined at 400 °C showed better catalytic activity than those supported on TiO₂ calcined at 500 and 700 °C. Among all our investigated catalysts with CuO loading from 2% to 12%, the catalyst with 8 wt% CuO loading exhibited the highest catalytic activity. The optimum calcination temperature of the CuO/TiO₂ catalysts was 300 °C. The XRD results indicated that the catalytic activity of the CuO/TiO₂ catalysts was related to the crystal phase and particle size of TiO₂ support and CuO active component.     

Selective hydrogenation of cinnamaldehyde using Pd catalysts supported on Mg/Al mixed oxides: Influence of the Pd incorporation method

A series of hydrotalcite‐like compounds was synthesized by varying Mg/Al molar ratio with values of 2, 3, and 4. After thermal treatment at 823 K, the corresponding mixed oxides were obtained and used as catalytic supports. The incorporation of a Pd metallic phase (0.5 g/g loading), was carried out by two methods: 1) in situ vapour phase thermal decomposition, and 2) impregnation by organic method. Fresh and calcined samples were characterized by XRD and N₂ sorption experiments. The basic and metal functions were analyzed by CO₂‐TPD and H₂‐TPR. The Pd‐support interaction was studied by FTIR spectroscopy using CO as a probe molecule while the morphology of Pd nanoparticles on the catalysts was studied by SEM, HRTEM, and theoretical simulation using the Fast Fourier Transform (FFT) method. Finally, the catalytic activity results showed a higher conversion towards hydrocinnamaldehyde in the cinnamaldehyde hydrogenation reaction for the catalysts prepared by vapour phase thermal decomposition, compared with those prepared by organic method, showing the significant dependence on the catalytic activity and the Pd incorporation method.     

Ni–Mo and Ni–W sulfide catalysts prepared by decomposition of binary thiometallates

Ni–Mo and Ni–W sulfide catalysts with atomic ratio R = 0.5 (Ni/(Ni + M), with M = Mo or W) prepared by decomposition of Ni-impregnated thiometallates were evaluated in the reaction of thiophene hydrodesulfurization. Catalysts derived from impregnated thiometallates (DTI samples) presented improved catalytic activity and higher synergistic effect than catalysts prepared by co-precipitation (HSP samples) despite the fact that co-precipitated catalysts showed larger surface area. Structure characterization by high-resolution electron microscopy (HREM) and X-ray diffraction (XRD) revealed different crystalline phases in DTI and HSP catalysts. A mixture of phases (MS₂, NiS_1.03 and MO₂) was observed in catalysts obtained by co-precipitation. Only the poorly crystalline MS₂ phase was observed in DTI catalysts suggesting that the Ni promoter is very well dispersed on the chalcogenide structure.     

Carbon dioxide reforming of methane to synthesis gas over hexaaluminate ANiAl11O19-delta (A = Ca, Sr, Ba and La) catalysts

A series of A‐modified hexaaluminates, ANiAl₁₁O_19-δ (A = Ca, Sr, Ba and La) as new catalysts for carbon dioxide reforming of methane to synthesis gas, were prepared by decomposition of nitrates and calcination at high temperature. Nickel ions as active component were inlayed in the hexaaluminate lattices to substitute part of Al ions. The structure and properties of these samples were characterized using XRD, XPS, TPR and TGA techniques. The series of hexaaluminates exhibited significantly catalytic activity and stability at high temperature, for instance at 780°C for 18 h, the conversion of CH₄ and CO₂ was kept over 91.0 and 93.7%, respectively, meanwhile no Ni sintering, phase transformation and catalyst deactivation due to carbon deposition were found. Besides, the modifier A in the mirror plane layer of the lattices showed different effects on reducibility and catalytic activity of transition metal Ni in the hexaaluminate lattices. This revised version was published online in July 2006 with corrections to the Cover Date.     

Copper oxide catalysts supported on ceria for low-temperature CO oxidation

Copper oxide catalysts supported on ceria were prepared by wet impregnation method using finely CeO₂ nanocrystals, which was derived from alcohothermal synthesis, and copper nitrate dissolved in the distilled water. The catalytic activity of the prepared CeO₂ and CuO/CeO₂ catalysts for low-temperature CO oxidation was investigated by means of a microreactor-GC system. The samples were characterized using BET, XRD, SEM, HRTEM and TPR.     

An investigation into the effect of Cs promotion on the catalytic activity of NiO in the direct decomposition of N2O

A series of Cs promoted NiO catalysts have been prepared and tested for direct decomposition of N₂O. These catalysts are characterized by BET surface area, X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption of N₂O (TPD-N₂O) and X-ray photo electron spectroscopy (XPS). The Cs promoted NiO catalysts exhibit higher activity for the decomposition of N₂O compared to bulk NiO. The catalyst with Cs/Ni ratio of 0.1 showed highest activity. The enhancement in catalytic activity of the Cs promoted catalysts is attributed to the change in the electronic properties of NiO. The characterization techniques suggest weakening of Ni–O bond thereby the desorption of oxygen becomes more facile during the reaction. The Cs promoted NiO catalyst is effective at low reaction temperature and also in the presence of oxygen and steam in the feed stream. IICT Communication No: 070523.     

Characterization of aerogel Ni/Al2O3 catalysts and investigation on their stability for CH4-CO2 reforming in a fluidized bed

The CH₄-CO₂ reforming was investigated in a fluidized bed reactor using nano-sized aerogel Ni/Al₂O₃ catalysts, which were prepared via a sol–gel method combined with a supercritical drying process. The catalysts were characterized with BET, XRD, H₂-TPR and H₂-TPD techniques. Compared with the impregnation catalyst, aerogel catalysts exhibited higher specific surface areas, lower bulk density, smaller Ni particle sizes, stronger metal-support interaction and higher Ni dispersion degrees. All tested aerogel catalysts showed better catalytic activities and stability than the impregnation catalyst. Their catalytic stability tested during 48 h reforming was dependent on their Ni loadings. Characterizations of spent catalysts indicated that only limited graphitic carbon formed on the aerogel catalyst, while massive graphitic carbon with filamentous morphology was observed for the impregnation catalyst, leading to significant catalytic activity degradation. An aerogel catalyst containing 10% Ni showed the best catalytic stability and the lowest rate of carbon deposition among the aerogel catalysts due to its small Ni particle size and strong metal-support interaction.     

Catalytic combustion of benzene over supported metal oxides catalysts

Catalytic combustion of benzene over supported metal oxides has been investigated. The catalysts have been prepared by incipient wetness method and characterized by XRD, FT-Raman, ESR and TPR. Among supported metal oxides, CuO_x, supported on TiO₂ is found to have the highest activity for benzene oxidation. In addition, among the catalysts of copper oxide supported on TiO₂, A1₂O₃ and SiO₂, titania-supported catalyst (CuO_x/TiO₂) gives the highest catalytic activity. CuO_x/TiO₂ (Cu loading 5.5 wt%) shows the total oxidation of benzene at about 250 °C. From the ESR and FT-Raman results, the CuO dispersed on the TiO₂ surface acts as an active site of CuO_x/TiO₂ catalysts on the oxidative decomposition of benzene. The catalytic activity gradually increases with an increase of Cu loading on TiO₂. When Cu loading reaches 5.5 wt%, the total conversion temperature is lowered to 300 °C. However, the catalytic activity considerably decreases at 7 wt% Cu loading. The catalytic activity increased with an increase of oxygen concentration but the concentration of benzene showed no difference in the benzene conversion. This result suggests that the rate determining step is the adsorption of oxygen.     

Comparison of CuO/Ce0.8Zr0.2O2 and CuO/CeO2 Catalysts for Low-temperature CO Oxidation

CuO/Ce_0.8Zr_0.2O₂ and CuO/CeO₂ catalysts were prepared via a impregnation method characterized by using FT-Raman, XRD, XPS and H₂-TPR technologies. The catalytic activity of the samples for low-temperature CO oxidation was investigated by means of a microreactor-GC system. The influence of the calcination temperature and different supports on the catalytic activity was studied.     

Effect of preparation method and particle size on LaMnO3 performance in butane oxidation

LaMnO₃ with different crystal domain sizes and surface areas were prepared by citrate and sol-gel combustion methods and tested as catalysts for butane total oxidation reaction. The catalysts were characterized by N₂ physisorption, XRD and SEM. LaMnO₃ with crystal domain sizes in the range of 30–90 nm were detected by XRD characterization when high calcination temperature, at least 500 °C for sol-gel combustion method and 700 °C for citrate method, was required to prepare pure nanocrystalline phase. Although LaMnO₃ prepared by these two methods had similar crystal domain sizes, BET surface areas of samples by citrate method were significantly larger than that of samples prepared by combustion method. The difference of surface area lies in the morphology differences between the two series of samples (SEM micrographs) generated by strong sintering of samples prepared by combustion method. The catalytic activity of LaMnO₃ in butane total oxidation increased with increasing surface area being higher for materials prepared by citrate method. Thus, citrate method showed significant advantages over combustion method in preparation of perovskite catalysts.     

Highly active and coking resistant Ni/CeO2-ZrO2 catalyst for partial oxidation of methane

Nickel catalysts over the CeO₂-ZrO₂ solid solution were successfully prepared by the co-precipitation method for partial oxidation of methane. The structures of the catalysts were systematically examined by N₂ adsorption/desorption, CO chemisorption, X-ray diffraction (XRD) and H₂-TPR techniques. The catalytic performance and carbon deposition were investigated for partial oxidation of methane as well. The results showed that the Ni/CeO₂-ZrO₂ catalysts had a large BET area and fine Ni dispersion. By the co-precipitation method, Ni and CeO₂-ZrO₂ solid solution had strong interaction confirmed by the H₂-TPR analysis. The Ni/CeO₂-ZrO₂ catalysts showed high activity and stability and the Ni/Ce_0.25Zr_0.75O₂ exhibited the best activity and coking resistance among these catalysts. The catalytic activities and coking resistant behaviors of catalysts were affected by the surface and structural properties of the catalysts.     

An Investigation of Catalytic Activity for CO Oxidation of CuO/Ce x Zr1–x O2 Catalysts

A series of CuO/Ce _x Zr_1–x O₂ catalyst powders with different Ce/Zr ratio were prepared via an impregnation method and characterized by X-ray diffraction (XRD), Fourier transform Raman (FT-Raman), H₂-Temperature-programmed reduction (TPR) and X-ray photoelectron spectra techniques. The catalytic properties of the catalysts were evaluated by means of a microreactor-GC system. XRD results showed that the addition of CuO had no effect on the crystalline lattice of the support. The structures of the Ce _x Zr_1–x O₂ samples were confirmed by XRD analyses and FT-Raman results. The H₂-TPR profiles for these catalysts had three peaks, which could be attributed to the reduction of three kinds of CuO species, i.e., the highly dispersed CuO, the larger CuO species and the bulk CuO. The TPR analyses and catalytic property tests indicated that the Ce/Zr ratio of CuO/Ce _x Zr_1–x O₂ had an effect on the dispersion degree of CuO and the catalytic activity of the catalysts.     

The preparation of Au/CeO2 catalysts and their activities for low-temperature CO oxidation

Au/CeO₂ catalysts prepared by co-precipitation (CP) and deposition-precipitation (DP) methods were tested for low temperature CO oxidation reaction. The structural characters and redox features of the catalysts were investigated by XRD, XPS and H₂-TPR. Their catalytic performances for low temperature CO oxidation were studied by means of a microreactor -GC system. It showed that the catalytic activities of Au/CeO₂ catalysts greatly depended on the preparation method. The catalysts prepared by DP method exhibited a surprisingly higher activity towards CO oxidation than that prepared by CP method. This may arise from the differences in the particle sizes of Au and redox properties of the catalysts. The low Au loading and the resistance to high temperature of DP-prepared catalyst made it more applicable.     

Synthesis and Catalytic Activity of Silver-Coated Perlite in the Reaction of Ozone Decomposition

Samples of Bulgarian perlite mineral deposit (natural alumino-silicate glass) in the Rhodope mountain were coated with Ag particles via a spray pyrolysis method. This method allows uniform distribution of the silver particles on the outer shell surfaces. SEM, XPS, FT-IR, and XRD methods were applied for characterization of the samples. The XRD investigations of the pristine samples revealed the formation of metallic silver and a small quantity of Ag₂O₃ phase. The presence of silver was also confirmed by XPS analysis. It was established that Ag/perlite composite prepared by spray pyrolysis is a promising catalyst for ozone decomposition. The high catalytic activity is preserved during the complete course of the catalytic reaction. After the catalytic activity test some structural and phase changes in the samples were observed. The XRD patterns of the ozonated samples proved the presence of metallic silver, AgO and Ag₂O₃ phases. The FT-IR analyses revealed that some bands, assigned to Si-O-Si stretching modes, were shifted to lower frequencies after the ozone decomposition test. In general, the spray pyrolysis method turned out to be a very suitable technique for preparation of highly active silver-coated perlite catalyst for efficient ozone removal.     

High-temperature close coupled catalysts Pd/Ce-Zr-M/Al2O3 (M = Y, Ca or Ba) used for the total oxidation of propane

A series of high-temperature close coupled catalysts Pd/Ce-Zr-M/Al₂O₃ (M = Y, Ca or Ba) were prepared by ultrasonic-assisted successive impregnation. The catalysts were subjected to a series of characterization measurements. The results of activity evaluation show that Y is the best promoter for propane total oxidation, especially at the calcination temperature of 1100 °C. It is interesting that although the BET specific surface areas and the dispersion of Pd species decrease, the Y-promoted catalyst calcined at 1100 °C shows higher catalytic activity than the corresponding one calcined at 900 °C and better sulfur-resisting performance. The results of TEM, TPHD and CO chemisorption indicate that Y can remarkably increase the dispersion of Pd species. However, the dispersion is hard to be connected with the activity increase as the calcination temperature is elevated from 900 to 1100 °C. The change of active phases and the interaction between Pd species and the supports may account for the activity enhancement. Combined with XRD, H₂-TPR and O₂-TPD results, it is deduced that the coexistence of metallic Pd and PdO species in the catalysts calcined at 1100 °C may be also favorable to C₃H₈ oxidation. In a word, Pd/Ce-Zr-Y/Al₂O₃ is indeed a promising high-temperature close coupled catalyst applicable to high temperature.     

Water gas shift reaction over Cu–Mn mixed oxides catalysts: Effects of the third metal

Highly efficient Cu–Mn spinel catalysts for water gas shift (WGS) reaction were achieved by a single step urea-nitrate combustion method. A series of doped Cu–Mn-M catalysts (M = Ce, Zr, Zn, Fe, Al) were prepared by the same method. Effects of dopants on WGS activity and stability of doped Cu–Mn catalysts were investigated. The doped catalysts were characterized by BET, XRD and TPR. XRD results showed that non-doped samples and Zr-doped samples are mainly composed of Cu_1.5Mn_1.5O₄ phase, while CuO, Cu₂O and Cu_1.5Mn_1.5O₄ for other doped samples. It was further found that WGS activities depend strongly on the natures of the dopant employed despite of their lower content, varying in the order of Zr > Fe > non-doped > Ce > Al > Zn. TPR profiles revealed that all dopants shift the reduction peaks to lower temperature region, indicating no direct correlation between WGS activity and the reducibility. In addition, Zr-doped Cu–Mn catalyst with 5 wt.% content showed the best catalytic performance and, optimal stability exposed to oxygen-stream and on-stream operation. It indicates that ZrO₂ is an effective promoter for Cu–Mn catalyst, and the catalytic performances are related to the existence of a Cu_1.5Mn_1.5O₄ phase and ease reducibility of the catalysts.     

Investigating the effect of metal oxide additives on the properties of Cu/ZnO/Al2O3 catalysts in methanol synthesis from syngas using factorial experimental design

The Cu/ZnO/Al₂O₃ catalysts, prepared by co-precipitation method, have been modified by adding small amount of Mn, Mg, Zr, Cr, Ba, W and Ce oxides using design of experiments (1/16 full factorial design). The structure and morphology of catalysts were studied by X-ray diffraction (XRD) and BET. Performance of the prepared catalysts for CO/CO₂ hydrogenation to methanol was evaluated by using a stainless steel fixed-bed reactor at 5 MPa and 513 K. The oxide additives were found to influence the catalytic activity, dispersion of Cu, Cu crystallite size, surface composition of catalyst and stability of catalysts during their operations. The results showed that the Mn and Zr promoted catalysts have high performance for methanol synthesis from syngas.     

Oxidative methanol steam reforming (OSRM) on a PdZnAl hydrotalcite derived catalyst

Catalytic systems for the oxidative methanol reforming (OSMR) with a 1% and 2% metal loading were prepared impregnating the spinel-oxide mixture (ZnAl₂O₄/ZnO) obtained by thermal decomposition of a Zn–Al hydrotalcite at 1173 K with palladium nitrate solution. The samples, after thermal treatment in reducing conditions, were characterized by TEM and XRD. The catalysts showed a quite good catalytic activity in the reaction under study with high methanol conversion and good selectivity to CO₂. The high activity and selectivity were attributed to the prevailing presence, on the catalyst surface, of a highly dispersed 1:1 PdZn alloy phase.     

Promoting effect of an aluminum emulsion on catalytic performance of Cu-based catalysts for methanol synthesis from syngas

Copper-based catalysts modified with aluminum precursors having different morphologies for methanol synthesis were prepared and the effect of the addition of aluminum emulsion on the characteristics of the catalyst was studied by using X-ray diffraction (XRD), temperature-programmed reduction (TPR) and differential thermal gravity (DTG). The experiment results show that the copper-based catalyst prepared by mixing a Cu-Zn precipitate with an amorphous aluminum emulsion prepared in advance by precipitating an aluminum salt with ammonia exhibits higher specific surface area and catalytic performance for methanol synthesis from synthesis gas. The catalysts thus prepared were found to have more (Cu,Zn)₂CO₃(OH)₂ phase, from which more Cu/Zn sosoloid was produced during calcination. More sosoloid phase produced and stronger synergy between Cu and ZnO were verified to enhance the activity of the catalyst for methanol synthesis.