CO TPR Research Articles

Ceria supported platinum catalyst for CO oxidation reaction: Importance of metallic active species ― Commemorating the 100th anniversary of the birth of Academician Guangxian Xu

Ceria supported platinum catalyst has now been widely studied due to its excellent activity for CO oxidation. However, the electron state of active metal center is still an open question. In this work, a ceria nanorod support was prepared and platinum (Pt) with 0.9 at% was deposited using an impregnation method to obtain Pt/CeO2 catalyst. With the help of “light-off” experiment and temperature-programmed reduction under CO (CO-TPR) test, the conclusion is proposed that the process of hydrogen reduction can enhance the activity of CO oxidation reaction for the generation of optimal active Pt site. An innovative near-situ X-ray absorption fine structure (XAFS) technique was used to investigate the chemical state of central Pt atom during the reaction process, clearly demonstrating that the high oxidized state of Pt does harm to the activity for CO oxidation while the relatively reductive Pt exhibits high activity, and the different oxidized state and chemical environment of Pt during every process has been identified. Furthermore, the activity of our Pt/CeO2 catalyst is superior to that of most of the previous reports about CO catalytic oxidation by Pt based catalyst. Moreover, the optimal active species (Pt–O4) have been identified after hydrogen reduction, which could be a possible key strategy to control the oxidation of Pt.

Origin of High Activity and Selectivity of CuO/CeO2 Catalysts Prepared by Solution Combustion Synthesis in CO-PROX Reaction

A CuO/CeO2 catalyst with 4 wt % CuO nominal content has been prepared by solution combustion synthesis (SCS) and characterized by ICP-MS, BET surface area analysis, XPS, HRTEM, and H2, and/or CO TPR. The catalyst, showing a rather homogeneous distribution of copper that strongly interacts with ceria, has been tested in CO-PROX reaction. The enhanced performance of the catalyst compared to that of an impregnated sample with the same copper loading has been explained by modeling the experimental CO2 temperature-programmed desorption (TPD) curve, which allowed the determination and quantification of different active sites. The temperature range of activity and the ratio of the amount of sites activating CO and H2 oxidation, respectively, estimated for the two catalysts through the model explain the superior performance of the sample prepared by SCS despite its lower surface area.

The effect of support pretreatment on activity of Ag/SiO2 catalysts in low-temperature CO oxidation

Silver supported on silica, prepared by impregnation method, was investigated using TEM, XRD, UV–vis spectroscopy, TPO, H2 TPR and CO TPR methods, and tested in low-temperature CO oxidation. To reveal the role of metal-support interaction, the Ag catalysts based on silica, pre-treated at 500 (SiO2-500) and 900°C (SiO2-900), were compared. Highly dispersed silver particles (1–4nm) were observed for both Ag/SiO2-500 and Ag/SiO2-900 catalysts. The highest amount of active oxidative species was determined for Ag/SiO2-900 catalysts using TPx methods. The high temperature (900°C) pretreatment of silica support is found favorable for formation of silver species active in O2 and CO activation and leads to increasing of catalytic activity in CO oxidation. The defect structure of Ag nanoparticles is a possible reason for high activity in low-temperature CO oxidation.

Causes of Activation and Deactivation of Modified Nanogold Catalysts during Prolonged Storage and Redox Treatments.

The catalytic properties of modified Au/TiO2 catalysts for low-temperature CO oxidation are affected by deactivation and reactivation after long-term storage and by redox treatments. The effect of these phenomena on the catalysts was studied by HRTEM, BET, SEM, FTIR CO, XPS and H2 TPR methods. The main cause for the deactivation and reactivation of catalytic properties is the variation in the electronic state of the supported gold, mainly, the proportion of singly charged ions Au+. The most active samples are those with the highest proportion of singly charged gold ions, while catalysts with a high content of trivalent gold ions are inactive at low-temperatures. Active states of gold, resistant to changes caused by the reaction process and storage conditions, can be stabilized by modification of the titanium oxide support with transition metals oxides. The catalyst modified with lanthanum oxide shows the highest stability and activity.

Nanocrystalline Ferrihydrite-Based Catalysts for Fischer-Tropsch Synthesis: Part I. Reduction and Carburization Behavior.

Temperature-programmed reduction using H2 (H2-TPR) and CO (CO-TPR) was carried out to investigate the reduction and carburization behavior of nanocrystalline ferrihydrite-based Fe/Cu/K/SiO2 catalysts for use in Fischer-Tropsch synthesis (FTS). Unlike pure ferrihydrite, the ferrihydrite-based catalysts did not pass through the intermediate decomposition step of ferrihydrite (Fe9O2(OH)23) into hematite (a-Fe2O3) as they were reduced into magnetite (Fe3O4). This is attributed to the enhanced thermal stability induced by SiO2. For the ferrihydrite-based catalysts, the reduction of ferrihydrite into magnetite occurred in two stages because the reduction promoter, Cu, is not homogeneously distributed on the catalyst surfaces. The Cu-rich sites are likely to be reduced in the first stage, and the Cu-lean sites may be reduced in the second stage. After the ferrihydrite is reduced to magnetite, the reduction process of magnetite was similar to that for conventional hematite-based FTS catalysts: 'magnetite --> metallic iron' and 'magnetite --> wüstite (FeO) or fayalite (Fe2SiO4) --> metallic iron' in the H2 atmosphere; 'magnetite --> iron carbides' in the CO atmosphere.

Influence of Ce/Zr ratio on CO oxidation activity of ceria–zirconia supported Cu catalyst

The influence of Ce/Zr ratios in the cerium-rich region on the dispersibility and reduction property of Cu catalysts supported on ceria–zirconia composite oxides was investigated. In the catalysts, the dispersibility of copper oxide species on ceria–zirconia supports was different depending on Ce/Zr ratio. The particle size of copper oxide species on Ce0.7Zr0.3O2 was smaller than that on Ce0.5Zr0.5O2. CO oxidation activity of 1.0 wt % Cu/Ce0.7Zr0.3O2 was higher than that of 1.0 wt % Cu/Ce0.5Zr0.5O2. Temperature programmed reduction by CO (CO-TPR) measurement revealed that the reducibility of Cu/Ce0.7Zr0.3O2 was higher than that of Cu/Ce0.5Zr0.5O2. The temperature of the first peak in CO-TPR profiles for both catalysts was in good agreement with the temperature at which the conversion of CO reached 50% (T50). It is suggested that the copper oxide species — ceria–zirconia interaction influences the activation of oxygen at the interface between copper oxide species and ceria–zirconia, resulting in different catalytic performance for CO oxidation.

Dispersion effects of Ni2P catalysts on hydrotreating of light cycle oil

A series of Ni2P/SBA-15 catalysts with different Ni2P loadings were prepared and applied for the hydrotreating of light cycle oil. The loading level of Ni2P was varied from 0.5 to 3.0mmol Ni2P per 1.0g of SBA-15 support, resulting in the optimum catalyst loading of 2.0mmol Ni2P. The physical properties of the catalyst samples were characterized by N2-adsorption–desorption isotherms, CO uptake chemisorption, TPR, and TEM. X-ray diffraction (XRD) and extended X-ray absorption fine structure (XAFS) spectroscopy were used to obtain structural properties for the supported Ni2P catalysts. Hydrotreating tests were performed in a continuous flow fixed-bed reactor at 623K, 3.0MPa, and LHSV's of 0.5–1.0h−1. The 2.0mmol Ni2P/SBA-15 gave an HDS conversion of 99.0% and an HDN conversion of 92.5%, which were much higher than those of a Ni–Mo–S/Al2O3 catalyst which gave an HDS conversion of 91.9% and an HDN conversion of 65.8% based on the same LHSV of 0.5h−1. Substantial changes in the composition of aromatic compounds were found for the Ni2P/SBA-15 catalysts from 14.3wt.% 1-Ar (mono-aromatics), 40.6wt.% 2-Ar (di-aromatics) and 19.4wt.% 3+-Ar (tri+-aromatics) in the LCO feed to 46.1wt.% 1-Ar, 16.3wt.% 2-Ar and 2.0wt.% 3+-Ar in the product.

Surface and structural features of Pt/PrO2–Al2O3 catalysts for dry methane reforming

Pt catalysts supported on mixed PrO2–Al2O3 oxides with different PrO2 loading (1–20wt.%) were prepared by wetness impregnation method. The samples were characterized by XRD, XPS, UV–vis DRS, DRIFTS of CO adsorption, TPR and TEM. XRD analysis of the samples at high calcination temperature of 1023K showed that the size of Pt particles decreases with increasing the PrO2 content. TPR results exhibited a promoted synergetic effect between Pt and Pr oxide expressed by decreasing the reduction temperatures of both species. XPS and DRIFTS data demonstrated a charge transfer from Pt to Pr oxide species, creating Pt sites with different electron density. It was shown that the addition of praseodymium oxide to alumina-supported Pt catalyst leads to improvement of the catalytic activity and stability. It was found that 6wt.% is the optimal content of PrO2 to obtain high active Pt catalysts.

Silica supported copper and cerium oxide catalysts for ethyl acetate oxidation

The formation of active sites in the silica supported copper and cerium oxide bi-component catalysts for total oxidation of ethyl acetate was studied by Nitrogen physisorption, XRD, XPS, UV–Vis, Raman, FTIR of adsorbed CO spectroscopies and TPR. It was found that the interaction between the copper oxide nanoparticles and the supported on the silica ceria ones is realized with the formation of interface layer of penetrated into ceria lattice copper ions in different oxidative state. This type of interaction improves the dispersion of copper oxide particles and provides higher accessibility of the reactants to the copper active sites even at low copper amount.

Effect of the transition metal oxide supports on hydrogen production from bio-ethanol reforming

We studied the effect of transition metal oxides on hydrogen production from bio-alcohols on a series of Pt catalysts supported on activated carbon, ZrO2, TiO2 and CeO2 nanoparticles. These catalysts were synthesized with incipient wetness impregnation method and were characterized with CO pulse chemisorption, TPR, TPD, TPO, and synchrotron-based X-ray diffraction and X-ray absorption techniques. The activity of the catalysts for bio-alcohol reforming with steam/carbon ratio of 3/2 was tested using a fixed bed flow reactor system. Transition metal oxide supports affect the hydrogen production activity and selectivity significantly. The results indicate that the active sites for hydrogen production from reforming bio-alcohols are the sites where there exists strong synergistic interaction between Pt and oxygen vacancies in transition metal oxide nanoparticles. This interaction affects the electronic and structural properties of Pt and transition metal oxide nanoparticles. The higher activity and better stability with less coke formation are seen over the catalyst that has stronger Pt and oxygen vacancy interaction and weaker surface acidity. This work provides us insight to prepare a better catalytic system for bio-alcohol reforming process.

Influence of phosphate addition on activity of Ag and Cu catalysts for partial oxidation of alcohols

Phosphate-containing silica-supported silver and copper catalysts prepared by impregnation method were investigated using TEM, H2 TPR and CO TPR methods and tested in the reaction of selective ethylene glycol oxidation into glyoxal. It was shown that reversible oxidation–reduction of the active component took place in case of Ag- and Cu-containing catalysts. In case of Cu-containing systems formation of copper oxides on the catalyst surface led to the decrease in catalytic activity. Silver oxide-like species did not form in the presence of phosphate modifier on the surface of Ag-containing systems, and that led to the increase in glyoxal selectivity during ethylene glycol oxidation.

Alumina contribution to CO oxidation: A TPR and IR study

The alumina contribution to CO oxidation in the absence of O 2 on metal oxide supported catalysts was investigated by CO TPR and in-situ FTIR and DRIFT studies up to 800 °C. These tests were performed on two Al 2O 3 supported catalysts (1 wt.% Pt/La/γ-Al 2O 3 and 8 wt.% Cu/γ-Al 2O 3) and on two corresponding alumina supports (5 wt.% La 2O 3 stabilised γ-Al 2O 3 and high mechanical resistant spherical γ-Al 2O 3 particles). The quantitative determination of CO consumption and CO 2 and H 2 formation on the alumina supports was in agreement with a WGS reaction occurring between surface OH and CO with a predominantly 2:1 stoichiometry. In the CO TPR of metal oxide supported catalysts, in addition to the reduction of the metal, a WGS reaction took place with enhanced kinetics. This enhancement was the result of a CO spillover phenomenon from the metal to alumina hydroxyls. This phenomenon significantly affected the evaluation of the reduction degree of the supported metal and could not be neglected in the subsequent calculations.

Pd–Cu/AC and Pt–Cu/AC catalysts for nitrate reduction with hydrogen: Influence of calcination and reduction temperatures

The influence of calcination and reduction temperatures on the catalytic properties of Pd–Cu and Pt–Cu bimetallic catalysts supported on activated carbon for the reduction of nitrates was studied. The catalysts were prepared using different calcination and reduction temperatures, and the respective activities and selectivities for the reduction of nitrates in water with hydrogen were assessed. It was found that the different preparation conditions lead to different catalytic performances. For both catalysts, the activity decreases by increasing calcination and reduction temperatures, whereas the effect on the selectivity is not uniform. For the 1%Pd–0.3%Cu (wt.%) catalyst, the nitrate conversion after 5 h of reaction varies from 93% (sample calcined at 200 °C and not reduced) to 25% (sample calcined and reduced at 400 °C). The formation of alloys during the preparation of the catalysts is prejudicial for nitrate reduction. In all the preparation conditions tested the Pd–Cu pair is more selective for the transformation of nitrate into nitrogen. All the samples have been characterized by nitrogen adsorption at −196 °C, CO adsorption microcalorimetry, TPR, XRD, XPS and TEM.

Promotional effect of potassium on soot oxidation activity and SO2-poisoning resistance of Cu/CeO2 catalyst

Abstract Potassium nitrate was incorporated to the Cu/CeO2 system to enhance the soot oxidation activity and sulfur-poisoning resistance. The Cu, K/CeO2 catalyst exhibited superior activity for soot oxidation with the lowest Tm at 313 and 359 °C under tight and loose contact modes, respectively. The CO–TPR curves demonstrated that the co-impregnation of copper and potassium effectively shifted the redox process of ceria to lower temperatures, contributing greatly to enhance soot oxidation activity. The IR spectra of SO2 poisoned catalysts implied partial transformation of KNO3 to K2SO4. The activity loss of the binary metal catalysts by SO2 poisoning was less than 70 °C thanks to remained KNO3.

Effect of interaction between potassium and structural promoters on Fischer–Tropsch performance in iron-based catalysts

The Fischer–Tropsch synthesis (FTS) performances of iron-based catalysts promoted with/without potassium compounds containing different acidic structural promoters (Al 2O 3, SiO 2, and ZSM-5) were studied in this research. Characterization technologies of temperature-programmed reduction with CO (CO-TPR), powder X-ray diffraction (XRD) and Mössbauer effect spectroscopy (MES) were used to study the effect of K–structural promoter interactions on the carburization behaviors of catalysts. It showed that the addition states of potassium (K–Al 2O 3, K–SiO 2, K–ZSM-5 and K-free) have a significant influence on the formation of iron carbides, which shows a following sequence in promotion of carburization: K–Al 2O 3 > K–SiO 2 > K–ZSM-5 > K-free. The FTS reaction test was performed in a fixed bed reactor. It is found that Fe/K–Al 2O 3 catalyst leads to the highest CO conversion, Fe/K–ZSM-5 catalyst shows the highest H 2 conversion, and Fe/K-free catalyst shows the lowest CO and H 2 conversion. As for the hydrocarbon selectivity, Fe/K–SiO 2 catalyst yields the lowest methane and the highest C 5 + products, Fe/K–ZSM-5 catalyst yields higher methane and the highest liquid hydrocarbon product, whereas Fe/K-free catalyst yields the highest methane and the lowest C 5 + products. These results can be explained from the interaction between potassium and structure promoters, and the spillover of reactants or intermediates from Fe sites to the surfaces of structural promoters.

Characterizations of Unsupported and Supported Rhodium−Iron Phosphate Catalysts Effective for Oxidative Carbonylation of Methane

Unsupported and MCM-41-supported Rh-doped FePO4 catalysts, which are effective for the oxidative carbonylation of methane directly to methyl acetate in the presence of CO and N2O, have been characterized by CO TPR in combination with XPS and FTIR spectroscopy of CO chemisorption. The CO TPR studies provide further evidence that the location of the Rh species is different in catalysts prepared by different methods. The CO TPR results and the correlation between the dispersion of the Rh species and the catalytic performance support the speculation that the dual sites containing RhIII and FeIII connected by phosphate groups are responsible for the conversion of methane to methyl acetate. The CO TPR studies also provide insight into the probable oxidation states of Rh and Fe during the catalytic reaction. We found that the RhIII and FeIII sites undergo simultaneous reductions during the reaction on the Rh−FePO4 sample prepared from a mixed aqueous solution and the MCM-41-supported Rh−FePO4 sample prepared by ...

Selective CO oxidation in the presence of hydrogen over supported Pt catalysts promoted with transition metals

Selective CO oxidation in the presence of excess hydrogen was studied over supported Pt catalysts promoted with various transition metal compounds such as Cr, Mn, Fe, Co, Ni, Cu, Zn, and Zr. CO chemisorption, XRD, TPR, and TPO were conducted to characterize active catalysts. Among them, Pt-Ni/γ-Al2O3 showed high CO conversions over wide reaction temperatures. For supported Pt-Ni catalysts, Alumina was superior to TiO2 and ZrO2 as a support. The catalytic activity at low temperatures increased with increasing the molar ratio of Ni/Pt. This accompanied the TPR peak shift to lower temperatures. The optimum molar ratio between Ni and Pt was determined to be 5. This Pt-Ni/γ A12O3 showed no decrease in CO conversion and CO2 selectivity for the selective CO oxidation in the presence of 2 vol% H2O and 20 vol% CO2. The bimetallic phase of Pt-Ni seems to give rise to stable activity with high CO2 selectivity in selective oxidation of CO in H2-rich stream.

Nanocrystalline Doped Ceria-Zirconia Fluorite-Like Solid Solutions Promoted by Pt: Structure, Surface Properties and Catalytic Performance in Syngas Generation

AbstractNanocrystalline ceria-zirconia samples doped with rare-earth (Gd, Pr, Sm, La) cations were prepared via modified Pechini route. Effect of their real structure and surface composition characterized by a combination of sophisticated physical methods (XRD, TEM +EDX, EXAFS, WAXS, UV-Vis, XPS, SIMS) on the mobility and reactivity of the lattice oxygen estimated by oxygen isotope exchange, H2, CH4 and CO TPR was analyzed. For the reaction of acetone autothermal reforming into syngas, catalytic activity correlates rather well with the oxygen mobility controlled by the type and content of a dopant

Effect of the surface/bulk doping of lanthanum manganite on the oxygen mobility, reactivity and catalytic activity in the CO oxidation

Dispersed samples of LaMnO 3 prepared by the Pechini method and annealed at 500°C were doped with cations of a different charge and size (Ce, Fe, Bi, Sr+Bi), while the sample surface was modified with Pt. The effects of the doping and of the surface modification on the oxygen mobility (as estimated by O 2 TPD) in the samples and on their reactivity (as estimated by CO TPR) as related to the catalytic activity in the CO oxidation are considered.

The role of Sn in Pt–Sn/CeO 2 catalysts for the complete oxidation of ethanol

The structural features and catalytic properties of Pt–Sn/CeO 2 catalysts prepared by modified polyol method were extensively investigated for the complete oxidation of ethanol. CO chemisorption, TPR, DTA and XPS measurements identically indicated that the electronic configuration of Pt by Sn as well as the formation of PtSn alloy were the key factors in determining the nature of the active sites. A strong Pt/Sn atomic ratio dependence of catalytic performances was observed, which was explained in terms of the changes in the surface structure of metal phases and the electronic Pt–Sn interaction.