Co‐Metal Catalysts on SiO2‐TiO2 for Methanol Production from CO2 – Effect of Preparation Methods

The effect of quantity, composition, and different impregnation sequences on the catalytic properties of Cu‐Zn‐Al/SiO₂‐TiO₂ in the CO₂ hydrogenation for methanol production was investigated. The Cu‐Zn‐Al catalysts supported on SiO₂ and TiO₂ were prepared by incipient wetness impregnation. Then, their performances in CO₂ hydrogenation were tested under defined conditions. The composition variation of Cu and Zn catalysts resulted in a high methanol production for Cu catalysts with a higher content of Cu, which was the active site for CO₂ activation. Regarding the metal quantity of catalysts, a relatively low loading of co‐metal (Cu‐Zn‐Al) led to the maximum methanol yield when compared with higher loadings as a result of the largest surface area.     

Methanol synthesis pathway over Cu/ZrO2 catalysts: a time‐resolved DRIFT 13C‐labelling experiment

X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) have been used to characterize a series of Cu/Ce/Al₂O₃ catalysts. Catalysts were prepared by incipient wetness impregnation using metal nitrate and alkoxide precursors. Catalyst loadings were held constant at 12 wt% CuO and 5.1 wt% CeO₂. Mixed oxide catalysts were prepared by impregnation of cerium first, followed by copper. The information obtained from surface and bulk characterization has been correlated with CO and CH₄ oxidation activity of the catalysts. Cu/Al₂O₃ catalysts prepared using Cu(II) nitrate (CuN) and Cu(II) ethoxide (CuA) precursors consist of a mixture of copper surface phase and crystalline CuO. The CuA catalyst shows higher dispersion, less crystalline CuO phase, and lower oxidation activity for CO and CH₄ than the CuN catalyst. For Cu/Ce/Al₂O₃ catalysts, Ce has little effect on the dispersion and crystallinity of the copper species. However, Cu impregnation decreases the Ce dispersion and increases the amount of crystalline CeO₂ present in the catalysts, particularly in Ce modified alumina prepared using cerium alkoxide precursor (CeA). Cerium addition dramatically increases the CO oxidation activity, however, it has little effect on CH₄ oxidation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cu/SiO2 catalyst prepared by electroless method

Cu/SiO₂ catalysts prepared by an electroless deposition method were investigated and compared with those by an impregnation method. Copper contents varied from 5% to 15% and SiO₂ was used as support. All catalysts were characterized by BET, DSC, SEM and TPR and tested by an n-butanol dehydrogenation reaction for activities and stabilities. BET analysis showed that the catalysts prepared by the two methods present larger average pore size and less surface area than those of the fresh SiO₂, indicating that smaller pores may get blocked during the course of preparation. This blockage is more severe in the impregnation method. SEM photos showed that the electroless method produces smaller copper crystals than the impregnated method. The reaction activity was found to be in the order of the calcined electroless copper catalyst>the fresh electroless copper catalyst>impregnated copper catalyst. © 1998 Society of Chemical Industry     

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.     

Evidence of a metal-support interaction in sol-gel derived Cu-ZrO2 catalysts for CO hydrogenation

Sol-gel derived Cu/ZrO₂ catalysts have recently been shown to have high activity and selectivity toward methanol synthesis. TPR, TEM, in situ XRD and N₂O decomposition have now been used to characterize the active sites in such catalysts over a wide range of Cu concentration. Copper is shown to be in two forms: surface aggregates (or particulate) and dispersed copper in the ZrO₂ substitutional sites. The proportion of the former increases with an increasing Cu content, while the overall strength of the Cu-ZrO₂ interaction simultaneously decreases. The activity in CO/CO₂ hydrogenation showed no evident correlation with the total Cu surface area, but rather with the concentration of highly-dispersed form of copper. This is taken to indicate that the copper in the substitutional sites of ZrO₂ is predominantly responsible for and associated with the active sites on Cu/ZrO₂ for CO/CO₂ hydrogenation.     

Effect of manganese on Cu/SiO2 catalysts for the dehydrogenation of cyclohexanol to cyclohexanone

The effect of the addition of manganese to Cu/SiO₂ catalysts for cyclohexanol dehydrogenation reaction was investigated. At reaction temperature of 250 °C, the conversion and the selectivity to cyclohexanone were both increased with the addition of manganese to Cu/SiO₂ catalyst. However, as the reaction temperature was further increased, higher loading of manganese in Cu/SiO₂ catalyst led to a decrease in the conversion of cyclohexanol. Manganese in Cu/ SiO₂ catalyst decreased the reduction temperature of copper oxide, increased the dispersion of copper metal, and decreased the selectivity to cyclohexene. It was found that the dehydration of cyclohexanol to cyclohexene occurred on the intermediate acid sites of catalyst. At high Mn loading, catalyst surface was more enriched with manganese in used catalyst compared to that in freshly calcined or reduced catalyst, which may account for the sharp decrease of the conversion at high temperature of 390 °C. Upon reduction, copper manganate on silica was decomposed into fine particles of copper metal and manganese oxide (Mn₃O₄).     

Liquid-phase transfer hydrogenation of furfural to furfuryl alcohol on Cu–Mg–Al catalysts

The liquid-phase transfer hydrogenation of furfural on Cu-based catalysts was studied. Catalysts were prepared by incipient wetness impregnation (Cu/SiO₂) and co-precipitation (Cu–Mg–Al). The effect of metal-support interaction, hydrogen donor, copper loading and temperature on catalytic performance was evaluated. Small particles, strongly interacting with a spinel-like matrix, had higher capability for transferring hydrogen than large ones having low interaction with support. An important increase in reaction rate was observed when temperature was raised from 110 to 150 °C. Thus, it was possible to attain complete furfural conversion to furfuryl alcohol with Cu(40%)–Mg–Al after 6 h at 150 °C.     

Dehydrogenation of cyclohexanol on Cu–ZnO/SiO2 catalysts: The role of copper species

For the dehydrogenation of cyclohexanol a series of Cu–ZnO/SiO₂ catalysts with various Cu to ZnO molar ratios was prepared using the impregnation method, with the loading of copper fixed at 9.5 at.%. The catalysts were characterized by XPS, H₂–N₂O titration, BET, H₂-TPR, NH₃-TPD and XRD techniques. The results indicate that the addition of ZnO can improve the dispersion of copper species on reduced Cu–ZnO/SiO₂ (CZS) catalysts. Cu⁰ and Cu⁺ species were found on the reduced CZS catalysts surface, and the amount of Cu⁺ increased with the content of ZnO increasing. The addition of ZnO increased the acidity of the CZS catalysts. However, only Cu⁰ species can be found on the reduced Cu/SiO₂ (CS) catalyst surface. According to the reaction results, we found that the selectivity to phenol was related to the amount of Cu⁺ species, the Cu⁺ species should be the active sites for the production of phenol, the Cu⁰ is responsible for cyclohexanol dehydrogenation to cyclohexanone.     

Support and additive effects in the synthesis of methanol over copper catalysts

Catalysts containing copper and ZnO in various combinations have been prepared, the copper surface areas have been measured by nitrous oxide frontal chromatography, and the activities in the reaction of CO/CO₂/H₂ and CO/H₂ mixtures to methanol have been determined at 250°C and 10 bar pressure. The results show that there is a strong synergy between copper and ZnO with the area specific rate of Cu/ZnO catalysts being about one order of magnitude larger than that of a Cu/SiO₂ catalyst. The synergy between copper and ZnO is observed both in the presence and absence of carbon dioxide. It is also observed that physical mixtures of Cu/SiO₂ and ZnO/SiO₂ catalysts are significantly more active than either of the components alone. The results are discussed in terms of possible interactions between copper and ZnO in the most active catalysts.     

Novel preparation method of highly active Co/SiO2 catalyst for Fischer-Tropsch synthesis with chelating agents

Co/SiO₂ catalysts were prepared by the incipient wetness method using the aqueous Co nitrate solution modified with various organic acids and/or chelating agents followed by drying and calcination. After H₂ reduction at 773 K, the catalyst prepared with nitrilotriacetic acid (NTA) showed Fischer-Tropsch synthesis (FTS) activity ca. 3 times higher than the catalyst without additives under mild reaction conditions (503 K, 1.1 MPa).     

Catalytic activity of copper-ceria catalysts supported on different zeolites for CO oxidation

Copper-ceria catalysts for CO oxidation supported on 4A, 5A, NaX and NaY zeolites were prepared by incipient wetness impregnation and excess-solution impregnation. Catalysts were characterized by SEM, EDX, XRD, N2 adsorption-desorption, H2-TPR and XPS. Results revealed that the catalysts were greatly affected by zeolites and preparation method. EDX results indicated the metal loading of 4A-ES (5.1 wt% Cu, 15.7 wt% Ce), 5A-ES (5.9 wt% Cu, 19.2% Ce), NaX-ES (11.7wt% Cu, 4.2 wt% Ce) and NaY-ES (11.0 wt% Cu, 7.9 wt% Ce) greatly varied. TPR results suggested that the peak at around 195 °C was presented in NaX-ES and 4A-IW, standing for dispersed copper species that is very active for CO oxidation. The catalytic activity of 4A-ES and NaX-ES was the best among catalysts made by excess-solution impregnation, demonstrated by the lowest T₅₀ at 127 and 129 °C, respectively. The catalytic activity of catalysts made by incipient wetness impregnation was worse than that of catalysts made by excess-solution impregnation, examined by the T₅₀ of 4A-IW and NaX-IW at 128 and 192 °C, respectively.     

Gas‐Phase Hydrogenolysis of Glycerol Catalyzed by Cu/MOx Catalysts

The catalytic activities of Cu/MO_x (MO_x = Al₂O₃, TiO₂, and ZnO) catalysts in the gas‐phase hydrogenolysis of glycerol were studied at 180–300 °C under 0.1 MPa of H₂. Cu/MO_x (MO_x = Al₂O₃, TiO₂, and ZnO) catalysts were prepared by the incipient wetness impregnation method. After reduction, CuO species were converted to metallic copper (Cu⁰). Cu/Al₂O₃ catalysts with high acidity, high specific surface areas and small metallic copper size favored the formation of 1,2‐propanediol with a maximum selectivity of 87.9 % at complete conversion of glycerol and a low reaction temperature of 180 °C, and favored the formation of ethylene glycol and monohydric alcohols at high reaction temperature of 300 °C. Cu/TiO₂ and Cu/ZnO catalysts exhibited high catalytic activity toward the formation of hydroxyacetone with a selectivity of approx. 90 % in a wide range of reaction temperature.     

Effect of the preparation method on the surface coverage of Mo/Al2O3 catalysts

Two series of Mo/Al₂O₃ catalysts were prepared by equilibrium adsorption and incipient wetness impregnation methods. The effect of preparation method on the surface coverages of the calcined catalysts was investigated by the combined use of CO₂ chemisorption, low temperature CO adsorption and ion scattering spectroscopy (ISS). For a given Mo loading, the CO₂ and CO adsorption results showed little difference between the two preparation methods. As previously noted, the CO₂ chemisorption method overestimated the Mo surface coverage. In contrast to the adsorption methods, the ISS technique gave different Mo surface coverage values for a given Mo content of the two series of catalysts. This apparent discrepancy was attributed to different repartition of the Mo phase between the internal and external surfaces which can only be detected by ISS. This interpretation is supported by the observed agreement between the coverage values measured from ISS and low temperature CO adsorption for presumably uniform catalysts obtained by the equilibrium adsorption method.     

Novel‐doped zinc oxide sorbents for low temperature regenerable desulfurization applications

Eight metal oxide sorbents including transition metal doped ZnO/SiO₂ sorbents and ZnO/SiO₂ were prepared by incipient wetness impregnation for regenerable desulfurization applications at low temperatures (i.e. room temperature). Among them, copper‐doped sorbent (Cu‐ZnO/SiO₂) demonstrated the highest saturation sulfur capacity of 0.213 g sulfur/g ZnO (54% of the theoretical capacity), which is twice that of ZnO/SiO₂ sorbent. Compared with ZnO/SiO₂, Cu‐ZnO/SiO₂ demonstrated superior desulfurization performance in a wide temperature range of 20–400°C. Due to the use of porous SiO₂ support, Cu‐ZnO/SiO₂ is highly regenerable. It can be easily regenerated in air at low temperatures, ca. 300–550°C, which are much lower than the typical regeneration temperatures of commercial ZnO sorbents. Cu‐ZnO/SiO₂ maintained its sulfur capacity during 10 cycles of regeneration/sulfidation. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Characterization and reductive amination of cyclohexanol and cyclohexanone over Cu/ZrO2 catalysts

Reductive amination of cyclohexanol/cyclohexanone was studied over copper catalysts supported on zirconia. The effect of copper loading and dispersion was studied on the activity and selectivity of the reaction. A series of zirconia supported copper catalysts with varying copper loadings (1–15 wt%) were prepared by incipient wet impregnation method. The catalysts were characterized by X-ray diffraction (XRD) and temperature-programmed reduction (TPR). Copper dispersion and metal area were determined by N₂O decomposition by passivation method. X-ray diffraction patterns indicate the presence of crystalline CuO phase from 4.0 wt% Cu on zirconia. TPR patterns reveal the presence of highly dispersed copper oxide at lower temperatures and bulk CuO at higher temperatures. The acid–base properties of catalysts were investigated by means of a model reaction cyclohexanol dehydrogenation to cyclohexanone and compare with the results of TPD of ammonia, which allows to measure the acid–base properties of the support and to investigate the changes in surface acidity or basicity, resulting from the metal impregnation.     

Nanodispersed Au/Al2O3 catalysts for low-temperature CO oxidation: Results of research activity at the Boreskov Institute of Catalysis

This paper presents some important results of the studies on preparation and catalytic properties of nanodispersed Au/Al₂O₃ catalysts for low-temperature CO oxidation, which are carried out at the Boreskov Institute of Catalysis (BIC) starting from 2001. The catalysts with a gold loading of 1–2 wt.% were prepared via deposition of Au complexes onto different aluminas by means of various techniques (“deposition-precipitation” (DP), incipient wetness, “chemical liquid-phase grafting” (CLPG), chemical vapor deposition (CVD)). These catalysts have been characterized comparatively by a number of physical methods (XRD, TEM, diffuse reflectance UV/vis and XPS) and catalytically tested for combustion of CO impurity (1%) in wet air stream at near-ambient temperature. Using the hydroxide or chloride gold complexes capable of chemical interaction with the surface groups of alumina as the catalyst precursors (DP and incipient wetness techniques, respectively) produces the catalysts that contain metallic Au particles mainly of 2–4 nm in diameter, uniformly distributed between the external and internal surfaces of the support granules together with the surface “ionic” Au oxide species. Application of organogold precursors gives the supported Au catalysts of egg shell type which are either close by mean Au particle size to what we obtain by DP and incipient wetness techniques (CVD of (CH₃)₂Au(acac) vapor on highly dehydrated Al₂O₃ in a rotating reactor under static conditions) or contain Au crystallites of no less than 7 nm in size (CLPG method). Regardless of deposition technique, only the Cl-free Au/Al₂O₃ catalysts containing the small Au particles (d_i ≤ 5 nm) reveal the high catalytic activity toward CO oxidation under near-ambient conditions, the catalyst stability being provided by adding the water vapor into the reaction feed. The results of testing of the nanodispersed Au/Al₂O₃ catalysts under conditions which simulate in part removal of CO from ambient air or diesel exhaust are discussed in comparison with the data obtained for the commercial Pd and Pt catalysts under the same conditions.     

Creation of the active site for methanol synthesis on a Cu/SiO2 catalyst

The effect of ZnO/SiO₂ in a physical mixture of Cu/SiO₂ and ZnO/SiO₂ on methanol synthesis from CO₂ and H₂ was studied to clarify the role of ZnO in Cu/ZnO-based catalysts. An active Cu/SiO₂ was prepared by the following procedure: the Cu/SiO₂ and ZnO/SiO₂ catalysts with a different SiO₂ particle size were mixed and reduced with H₂ at 523-723 K, and the Cu/SiO₂ was then separated from the mixture using a sieve. The methanol synthesis activity of the Cu/SiO₂ catalyst increased with the reduction temperature and was in fairly good agreement with that previously obtained for the physical mixture of Cu/SiO₂ and ZnO/SiO₂. These results indicated that the active site for methanol synthesis was created on the Cu/SiO₂ upon reduction of the physical mixture with H₂. It was also found that ZnO itself had no promotional effect on the methanol synthesis activity except for the role of ZnO to create the active site. The active site created on the Cu/SiO₂ catalyst was found not to promote the formation of formate from CO₂ and H₂ on the Cu surface based on in situ FT-IR measurements. A special formate species unstable at 523 K with an OCO asymmetric peak at ~1585 cm^-1 was considered to be adsorbed on the active site. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydrocracking of petroleum gas oil over NiW/MCM-48-USY composite catalyst

MCM-48-USY composite materials were prepared by coating USY zeolite by a layer of MCM-48 mesoporous material at different meso/microporous ratios (SiO₂/USY ratios of 0.1, 0.2, 0.3, 0.4, 0.5) and used as support for nickel and tungsten. The NiW/MCM-48-USY catalysts were prepared using the incipient wetness method. The prepared catalysts were characterized by TPD-TGA acidity, TGA thermal stability, BET surface area, pore volume, pore size, XRD, SEM and TEM and then tested for hydrocracking of petroleum gas oil at reaction temperature of 450 °C, contact time of 90 min and catalyst to gas oil ratio of 0.04. In all prepared samples, the catalyst activity and properties were improved with increasing SiO₂/USY ratio and found that maximum values of a total conversion and liquid product (total distillate fuels) were obtained at SiO₂/USY ratio of 0.5. Finally, the obtained results from hydrocracking of gas oil over composite MCM-48-USY catalysts were compared with those obtained over physically mixed USY and MCM-48 catalysts.     

Effects of catalyst composition on methanol synthesis from CO2/H2

Effects of catalyst composition have been studied for Cu/support and Cu/ZnO/supports in methanol synthesis from CO₂/H₂. A strong effect of support has been observed. Different supports brought about different behavior in temperature-programmed reduction of copper, different copper surface areas, and different catalytic activity and selectivity. It seemed possible to find catalyst supports that might perform better than commercial Cu/ZnO/Al₂O₃ catalysts. A correlation was observed between catalytic activity and the copper surface area which was varied by using different supports. However, the sup]>orts appeared to influence other catalytic properties as well, for example, the surface oxygen coverage.     

Cu/Al2O3 catalysts for soot oxidation: Copper loading effect

Cu/Al₂O₃ catalysts with metal loading from 0.64 to 8.8 wt.% have been prepared and characterized by different techniques: N₂ adsorption at −196 °C (BET surface area), ICP (Cu loading), XRD, selective copper surface oxidation with N₂O (Cu dispersion), TPR-H₂ (redox properties), and XPS (copper surface species). The catalytic activity for soot oxidation has been tested both in air and NO_x/O₂. The activity in air depends on the amount of easily-reduced Cu(II) species, which are reduced around 275 °C under TPR-H₂ conditions. The amount of the most active Cu(II) species increases with the copper loading from Cu_1% to Cu_5% and remains almost constant for higher copper loading. In the presence of NO_x, the first step of the mechanism is NO oxidation to NO₂, and the catalytic activity for this reaction depends on the copper loading. For catalysts with copper loading between Cu_1% and Cu_5%, the catalytic activity for soot oxidation in the presence of NO_x depends on NO₂ formation. For catalysts with higher copper loading this trend is not followed because of the low reactivity of model soot at the temperature of maximum NO₂ production. Regardless the copper loading, all the catalysts improve the selectivity towards CO₂ formation as soot oxidation product both under air and NO_x/O₂.