O2 Support Research Articles

Catalytic oxidation of carbon black under the conditions of a weak contact in the presence of M/Ce0.72Zr0.18Pr0.1O2, where m is platinum, palladium, and ruthenium

Nanodisperse M/Ce0.72Zr0.18Pr0.1O2 catalysts, where M is Pt, Pd, and Ru in amounts of 0.5, 1.0, and 2.0 wt %, for the afterburning of carbon black in the exhaust fumes of diesel engines under the conditions of a weak contact are synthesized. The structural, textural, and catalytic properties of the samples are studied by means of energy dispersive X-ray spectroscopy (EDX), synchrotron X-ray diffraction, X-ray absorption near-edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS), transmission electronic microscopy (TEM), low-temperature nitrogen adsorption, and thermogravimetric analysis-differential scanning calorimetry (TG-DSC). It is shown that metal-support interaction, growing in the order Pt → Pd → Ru, occurs as platinum metals are impregnated into the surface of a Ce0.72Zr0.18Pr0.1O2 support. Ruthenium-containing catalysts are the ones most active for the afterburning of carbon black, due not only by the nature of the impregnated component, but also to the relatively ill-defined metal-support interaction, as compared to platinum and palladium samples. An ∼190°C drop in the temperature of oxidation onset and an ∼120°C drop in the temperature of complete oxidation, relative to these same parameters for a support free of platinum group elements, is characteristic of these. The high activity of 0.5%Ru/Ce0.72Zr0.18Pr0.1O2 enables us to purify diesel exhausts of carbon black effectively while using relatively small amounts of the noble metal, making it possible to lower the price of catalyst converters of diesel exhausts.

Active oxygen-assisted NO-NO2 recycling and decomposition of surface oxygenated species on diesel soot with Pt/Ce0.6Zr0.4O2 catalyst

A Pt/Ce0.6Zr0.4O2 catalyst was synthesized by impregnating a Ce0.6Zr0.4O2 support with Pt(NO3)2 solution. This material exhibits higher catalytic activity than Pt/Al2O3 for soot oxidation under loose contact conditions in both NO + O2 and O2 atmospheres. The results show that the pronounced activity of this catalyst is attributed to a synergistic effect arising from the combination of Pt and Ce0.6Zr0.4O2 solid solution, leading to a remarkable increase in the availability of active oxygen at temperatures as low as 450 °C. The NONO2 recycling efficiency is improved over Pt/Ce0.6Zr0.4O2 catalyst, enhancing the ability of the NO2-soot reaction to generate surface oxygenated complexes (SOCs) on the soot. More importantly, the catalytic oxidation of these SOCs can be accelerated with the participation of active oxygen from the CeO2-ZrO2 solid solution. As a result, during soot oxidation under NO + O2, the light-off temperature of the Pt/Ce0.6Zr0.4O2 catalyst is lowered by 34 °C than that of Pt/Al2O3 catalyst.

Renewable hydrogen production from oxidative steam reforming of bio-butanol over CoIr/CeZrO2 catalysts: Relationship between catalytic behaviour and catalyst structure

Several bimetallic CoIr/Ce0.82Zr0.18O2 catalysts with supports of different characteristics were studied in the oxidative steam reforming of a bio-butanol raw mixture (n-butanol/acetone/ethanol=6/3/1, mass ratio). Ce0.82Zr0.18O2 supports were prepared by precipitation and then calcination at different temperatures (500°C, 700°C and 900°C). The calcination temperature of the support determined certain characteristics of the final catalyst, namely: BET surface area, crystallite size, basicity, reduction properties and oxygen storage capacity (OSC). All of these factors were found to affect the performance of the catalysts in terms of: raw mixture conversion, hydrogen selectivity and resistance to deactivation upon long-term testing. Several techniques such as XRD, TPR, CO2 TPD, CO2 adsorption calorimetry, Raman, DRIFT, TEM, XPS and OSC were used to characterize the catalysts. Characterization of samples before and after catalytic tests allowed us to determine the influence of the catalyst characteristics on the deactivation process.

Comparison of flame-made rhodium on Al2O3 or Ce0.5Zr0.5O2 supports for the partial oxidation of methane

Catalytic partial oxidation of methane (CPOM) was investigated for rhodium supported on Al2O3 or on Ce0.5Zr0.5O2. The catalysts were synthesized by flame spray pyrolysis and characterized by nitrogen adsorption, transmission electron microscopy, X-ray diffraction, temperature-programmed reduction (TPR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The Rh/Al2O3 catalysts exhibited an enhanced and stable CPOM activity compared to Rh/Ce0.5Zr0.5O2. Syngas formation was promoted for 0.5wt% Rh on Al2O3 close to the calculated thermodynamic equilibrium, outperforming 1wt% Rh/Ce0.5Zr0.5O2 in the temperature range 525–750°C. A proposed mechanism of the effect of support on Rh activity is discussed in terms of oxygen transport capacity of the support materials. Further, high oxygen concentrations showed that Al2O3 is a better support compared to Ce0.5Zr0.5O2. This could be attributed to the fact that the Al2O3 support inhibits Rh oxidation and therefore allows the presence of Rh in its metallic state, which is preferable for high syngas formation. After thermal treatment of the catalysts, the catalytic effectiveness of Rh was more than 5 times higher for Al2O3 than for Ce0.5Zr0.5O2 supports.

A DFT study on CO oxidation on Pd4 and Rh4 clusters and adsorbed Pd and Rh atoms on CeO2 and Ce0.75Zr0.25O2 supports for TWC applications

CO oxidation reaction mechanisms and energetics are examined on adsorbed Pd4 and Rh4 clusters and adsorbed Pd and Rh atoms on CeO2 and Ce0.75Zr0.25O2 support structures using DFT methods. Activation barriers and TS structures are computed with CI-NEB method. On cluster adsorbed systems, Zr affects CO binding position and O2 adsorption mode. Energetically, formation of two CO2 molecules without barrier and surface regeneration is possible only on Pd4-CeO2 surface. With metal atom substituted surfaces, Pd substituted Ce0.75Zr0.25O2 and CeO2 supports are found to be capable of completing catalytic cycle with consecutive CO oxidations by creating and filling surface oxygen vacancies.

Ta Modified TiO2 Supports Exhibit Exceptional Durability in Polymer Electrolyte Fuel Cells

Ta modified TiO2 was synthesized using a sol-gel procedure and evaluated for use as an electrocatalyst support. Of the materials evaluated, Ta0.3Ti0.7O2 exhibited remarkably high stability under aggressive potential cycling tests designed to mimic harsh automotive drive cycles. The capacitance of the Ta0.3Ti0.7O2 support changed by 12% whereas the pseudocapacitance of a carbon benchmark changed by over 100% under identical test conditions. Pt/Ta0.3Ti0.7O2 electrocatalyst prepared by catalyzing this support showed high electrochemical stability which was attributed to a strong metal support interaction (SMSI); and fairly good performance. The stability of the catalyzed supports were evaluated by monitoring the evolution of the electrochemical surface area (ECSA) under potential cycling, loss in ECSA of Pt/Ta0.3Ti0.7O2 was found to be 35% compared to 46% for Pt/C over 10,000 load cycles. Pt/Ta0.3Ti0.7O2 showed fairly good performance: the electrochemical surface area of this electrocatalyst was 41 m2/g, while the mass activity and area-specific activities for the oxygen reduction reaction (ORR) were 62 mA/mgPt and 151 µA/cm2 Pt, respectively, as ascertained from electrochemical experiments performed on a rotating disk electrode (RDE). Based on these results, we propose that Ta0.3Ti0.7O2 is an excellent corrosion-resistant alternative to carbon as an electrocatalyst support.

OH Radical-Initiated Chemistry of Isoprene in Aqueous Media. Atmospheric Implications

The fate of isoprene (2-methyl-1,3-butadiene, ISO) emissions into the atmosphere is not fully understood. Increasing awareness that ISO is only partially processed in the gas-phase has turned attention to its reactive uptake by fog, cloud, and aerosol droplets. A hydrophobic gas, ISO would preferentially partition to the surface rather than the bulk of aqueous media. Such media normally contain dissolved O2 and water-soluble unsaturated organics and support •OH generation rates (from the solar photolysis of dissolved H2O2) that are several orders of magnitude larger than in the gas-phase. Thus, ISO should be converted therein to heavier products rather than into the C4-C5 volatile compounds produced in the gas-phase. Here we substantiate such a scenario by reporting that the λ > 305 nm photolysis of H2O2 in dilute aqueous ISO solutions yields C10H15OH species as primary products, whose formation both requires and is inhibited by O2. A minimum of seven C10H15OH isomers are resolved by reverse-phase high-performance liquid chromatography and detected as MH(+) (m/z = 153) and MH(+)-18 (m/z = 135) signals by electrospray ionization mass spectrometry. Our findings are consistent with the addition of •OH to ISO, followed by HO-ISO• reactions with ISO in competition with O2, leading to second generation HO(ISO)2• radicals that terminate as C10H15OH via β-H abstraction by O2. We show that a significant fraction of gas-phase olefins should be converted into less volatile species via this process on wet airborne particles.

Total oxidation of dichloromethane and ethanol over ceria–zirconia mixed oxide supported platinum and gold catalysts

Ce0.5Zr0.5O2 prepared by sol–gel method was used as a support for platinum and gold catalysts that were tested in total oxidation of dichloromethane and ethanol. It was shown that the deposition of platinum and gold on Ce0.5Zr0.5O2 support enhanced the reducibility of surface ceria. This phenomenon was more pronounced for platinum catalysts. Introduction of both noble metals led to the decrease of catalysts’ acidity. In total oxidation of dichloromethane, the noble metal catalysts showed lower catalytic performance compared to parent Ce0.5Zr0.5O2, due to lower amount of acid sites that act as chemisorption sites for chlorinated compounds. On the other hand, platinum catalysts exhibited significantly enhanced selectivity to CO2 in comparison with the Ce0.5Zr0.5O2 support. In total oxidation of ethanol, the deposition of platinum on Ce0.5Zr0.5O2 resulted in a significant increase in catalytic performance, while the introduction of gold had only a minor effect. Moreover, the positive effect of higher noble metal loading on catalytic performance was more pronounced for Pt catalysts. For all investigated catalysts, the temperature of the H2-TPR peak corresponding to the reduction of surface ceria correlated with their catalytic performance. The influence of Pt loading on the mechanism of ethanol oxidation was revealed. Based on the concentration profiles of individual by-products/products detected by on-line FTIR analysis, the possible pathways of their formation were suggested. Both noble metal catalysts exhibited higher selectivity to CO2 than the pristine Ce0.5Zr0.5O2.

DRIFTS studies on CO and NO adsorption and NO + CO reaction over Pd2+-substituted CeO2 and Ce0.75Sn0.25O2 catalysts

Sequential adsorption of CO and NO as well as equimolar NO+CO reaction with variation of temperature over Pd2+ ion–substituted CeO2 and Ce0.75Sn0.25O2 supports has been studied by DRIFTS technique. The results are compared with 2at.% Pd/Al2O3 containing Pd0. Both linear and bridging Pd0–CO bands are observed over 2at.% Pd/Al2O3. But, band positions are shifted to higher frequencies in Ce0.98Pd0.02O2−δ and Ce0.73Sn0.25Pd0.02O2−δ catalysts that could be associated with Pdδ+–CO species. In contrast, a Pd2+–CO band at 2160cm−1 is observed upon CO adsorption over Ce0.98Pd0.02O2−δ and Ce0.73Sn0.25Pd0.02O2−δ catalysts pre-adsorbed with NO and a Pd+–CO band at 2120cm−1 is slowly developed on Ce0.73Sn0.25Pd0.02O2−δ over time. An intense linear Pd0–NO band at 1750cm−1 found upon NO exposure to CO pre-adsorbed 2at.% Pd/Al2O3 indicates molecular adsorption of NO. On the other hand, a weak Pd2+–NO band at 1850cm−1 is noticed after NO exposure to Ce0.98Pd0.02O2−δ catalyst pre-adsorbed with CO indicating dissociative adsorption of NO which is crucial for NO reduction. Pd0–NO band is initially formed over CO pre-adsorbed Ce0.73Sn0.25Pd0.02O2−δ which is red-shifted over time along with formation of Pd2+–NO band. Several intense bands related to nitrates and nitrites are observed after exposure of NO to fresh as well as CO pre-adsorbed Ce0.98Pd0.02O2−δ and Ce0.73Sn0.25Pd0.02O2−δ catalysts. Ramping the temperature in a DRIFTS cell upon NO and CO adsorption shows the formation of N2O and NCO surface species, and N2O-formation temperature is comparable with the reaction done in a reactor.

Electrochemical oxidation of methanol on Pt/(RuxSn1-x)O2 nanocatalyst

The Ru-doped SnO2 powder, (RuxSn1-x)O2, with the Sn:Ru atomic ratio of 9:1 was synthesized and used as a support for Pt nanoparticles (30 mass% loading). The (RuxSn1-x)O2 support and Pt/(RuxSn1-x)O2 catalyst were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy and transmission electron microscopy (TEM). (RuxSn1-x)O2 was found to be two-phase material consisting of probably solid solution of RuO2 in SnO2 and pure RuO2. The average Pt particle size determined by TEM was 5.3 nm. Cyclic voltammetry of Pt/(RuxSn1-x)O2 indicated good conductivity of the sup-port and displayed usual features of Pt. The results of the electrochemical oxidation of COads and methanol on Pt/(RuxSn1-x)O2 were compared with those on commercial Pt/C and PtRu/C catalysts. Oxidation of COads on Pt/(RuxSn1-x)O2 starts at less positive potentials than on PtRu/C and Pt/C. Potentiodynamic polarization curves and chronoamperometric curves of methanol oxidation indicated higher initial activity of Pt/(RuxSn1-x)O2 catalyst compared to PtRu/C, but also a greater loss in the current density over time. Potentiodynamic stability test of the catalysts revealed that deactivation of the Pt/(RuxSn1-x)O2 and Pt/C was primarily caused by the poisoning of Pt surface by the methanol oxidation residues, which mostly occurred during the first potential cycle. In the case of PtRu/C the poisoning of the surface was minor and deactivation was caused by the PtRu surface area loss.

Effect of Reducing Agent on the Dispersion of Pt Nanoparticles on Electrospun Nb0.1Ti0.9O2 Nanofibers

ABSTRACTDegradation of the catalyst and catalyst support is an essential limitation of polymer electrolyte membrane (PEM) fuel cells containing commercial platinum on carbon catalysts. Catalysts based on platinum nanoparticles coated onto nanostructured TiO2 materials are presently investigated as a more stable and equally cost effective alternative. Reported here is the synthesis of two different Pt/Nb0.1Ti0.9O2 catalysts that were prepared by chemical reduction of H2PtCl6 with either sodium borohydride in ethanolic surfactant solution or ethylene glycol. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and high-resolution transmission electron microscopy confirmed the deposition of Pt nanoparticles on the surface of the nanofibers and revealed average sizes of 5.4 nm and 7.6 nm for reduction with ethylene glycol and sodium borohydride, respectively. The formation of smaller sized Pt nanoparticles in ethylene glycol is reasoned with the passivation of the nanoparticle surface by glycolic anions. Cyclic voltammetry measurements confirmed a higher electrochemical specific surface area (ESCA) of about 5.45 m2/gPt for the catalyst with smaller nanoparticles while the other catalyst reached only 4.96m2/gPt. Both catalysts retain about 60% of their electrochemically active surface area after 1000 voltammetric cycles in the range of 0.03 to 1.4 V vs. RHE. This relatively high value of activity retention is explained with a strong interaction between Pt nanoparticles and Nb0.1Ti0.9O2 support.

Ta0.3Ti0.7O2 Electrocatalyst Supports Exhibit Exceptional Electrochemical Stability

Tantalum (Ta) modified TiO2 was synthesized using a sol-gel procedure and evaluated for use as an electrocatalyst support. Platinum nanoparticles were deposited on this support via the incipient wetness method. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray energy dispersive spectroscopy (XEDS), X-ray photoelectron spectroscopy (XPS) and nitrogen desorption were used to investigate their microstructure. Of the formulations studied, Ta0.3Ti0.7O2 possessed an adequate powder electronic conductivity of 0.2 S/cm. The capacitance of this Ta0.3Ti0.7O2 support changed by only 12% whereas the pseudocapacitance of a carbon benchmark changed by over 100% over 10,000 support stability test cycles (support stability test protocol: 1.0-1.5 V vs. RHE at a scan rate of 500 mV/s in a 0.1 M HClO4 electrolyte at 25°C) under identical test conditions. The stability of 20% Pt/Ta0.3Ti0.7O2, 20% Pt/C, and 46% Pt/C (commercial, TKK) catalysts were evaluated by monitoring the evolution of the electrochemical surface area (ECSA) under load cycling (load cycling protocol: 0.6-0.95 V vs. RHE with a dwell time of 3 s at either potentials in a 0.1 M HClO4 electrolyte at 25°C). The loss in ECSA in 20% Pt/Ta0.3Ti0.7O2 was found to be 35% compared to 44-47% for 20% Pt/C and 46% Pt/C over 10,000 load cycles. 20% Pt/Ta0.3Ti0.7O2 yielded the following performance-related metrics: the ECSA of this electrocatalyst was 41 m2/g, the mass activity and area-specific activities for the oxygen reduction reaction (ORR) determined at 0.9 V vs. RHE in a 0.1 M HClO4 electrolyte at 25°C were 62 mA/mgPt and 151 μA/cm2Pt, respectively. Koutecky-Levich analysis carried out to evaluate ORR kinetics suggested that all 3 catalysts (20% Pt/Ta0.3Ti0.7O2, 20% Pt/C and 46% Pt/C) demonstrated similar ORR mechanisms. We propose that Ta0.3Ti0.7O2 shows outstanding promise as a corrosion-resistant alternative to carbon as an electrocatalyst support in polymer electrolyte fuel cells.

High-surface-area Ce0.8Zr0.2O2 solid solutions supported Ni catalysts for ammonia decomposition to hydrogen

Abstract Three kinds of Ce0.8Zr0.2O2 solid solutions synthesized via surfactant-assisted route, co-precipitation, and sol–gel method were used as supports of Ni-based catalysts by impregnation. Their catalytic activities in ammonia decomposition to hydrogen were tested, and the structural effect of support and the influence of nickel content on catalytic activity were evaluated. Mesoporous/high-surface-area Ce0.8Zr0.2O2 support synthesized by surfactant-assisted method exhibited better promoting effect than other supports when the same content of Ni was loaded. The interactions between Ni species and Ce0.8Zr0.2O2 supports were found to greatly affect the chemical properties of catalysts, including redox, H2 adsorption, and catalysis. The promoting effects of Ce in catalysts, plentiful vacancies in the solid solutions due to the doping of Zr4+, and high surface areas of the supports were discussed on the ammonia decomposition activities of the resultant catalysts, as well as the influence of hydrogen spillover. The ammonia conversion of 95.7% with the H2 producing rate of 89.3 mL/min·gcat was achieved at 550 °C over the Ni catalysts supported on the mesoporous/high-surface-area Ce0.8Zr0.2O2.

Surface structure characteristics of CuO/Ti0.5Sn0.5O2 and its activity for CO oxidation

CuO/Ti0.5Sn0.5O2 catalysts were prepared and characterized by high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible diffuse reflection spectrum (UV–vis DRS), electron paramagnetic resonance (EPR), laser Raman spectra (LRS), in situ infrared spectroscopy (IR), and activity test for CO oxidation. The results indicated that (1) copper oxide is highly dispersed on Ti0.5Sn0.5O2 support below its dispersion capacity of 0.85mmol Cu2+/100m2 Ti0.5Sn0.5O2; (2) three types of copper species are present on Ti0.5Sn0.5O2, which are isolated Cu2+, (CuOCu)2+ species, and crystalline CuO, respectively. Of them, the dispersed (CuOCu)2+ species are the easiest to be reduced by CO; (3) the catalytic activities of CuO/Ti0.5Sn0.5O2 catalysts are related to the state of copper on Ti0.5Sn0.5O2 support, and the dispersed (CuOCu)2+ species are the primary active component. A surface incorporation model was proposed to explain the CuO dispersion of CuO/Ti0.5Sn0.5O2 catalysts.

Advanced nanoelectrocatalyst for methanol oxidation and oxygen reduction reaction, fabricated as one-dimensional pt nanowires on nanostructured robust Ti0.7Ru0.3O2 support

We present a simple and facile approach to tackling many current fuel cell issues by exploiting the direct growth of 1D Pt nanowires on nanostructured multifunctional Ti0.7Ru0.3O2 that exploit various advantages conferred by the multifunctional Ti0.7Ru0.3O2 support when synergistically combined with 1D Pt nanowires. The robust non-carbon Ti0.7Ru0.3O2 not only plays an important role as a co-catalyst but also shows extremely high stability in acidic and oxidative environments. Furthermore, the unique 1D anisotropic morphology of the Pt nanostructures can improve mass transport and the preferential exposure of certain crystal facets so promoting the catalytic activity of Pt NW/Ti0.7Ru0.3O2 for both ORR and the Methanol Oxidation Reaction (MOR). We also show that the oxygen reduction reaction current densities at the half-wave potential (∼0.9V), generated using co-catalytic Pt NW/Ti0.7Ru0.3O2 are, respectively, ∼2-fold higher than those of commercial Pt/C (JM) catalyst or Pt NW on carbon. Additionally, Pt NW/Ti0.7Ru0.3O2 exhibited excellent electrocatalytic activity and CO-tolerance toward MOR. For example, at 600mV the polarization current density of Pt NW/Ti0.7Ru0.3O2 was ∼5 times and 8 times greater than for the Pt NW/C and Pt/C (JM) catalysts. Thus, Pt NW/Ti0.7Ru0.3O2 is a novel functionalised co-catalytic support that shows utility as an advanced nanoelectrocatalyst for both of anode and cathode fuel cell applications. This powerful approach opens a reliable path to the discovery of advanced multifunctional nanoelectrocatalysts that can replace the traditional catalytic structures and motivate further research in the field.

Highly dispersed supported ruthenium oxide as an aerobic catalyst for acetic acid synthesis

The increasing need for shifting to renewable feedstocks in the chemical industry has driven research toward using green aerobic, selective oxidation reactions to produce bulk chemicals. Here, we report the use of a ruthenium mixed oxide/hydroxide (RuOx) on different support materials for the selective aerobic oxidation of ethanol to acetic acid. The RuOx was deposited onto different oxide supports using a new gas-phase reaction, which in all cases resulted in homogeneous nanoparticulate films. The RuOx particle size ranged from 0.3 to 1.5nm. The catalytic activity was evaluated on TiO2, Mg6Al2(CO3)(OH)16·4(H2O), MgAl2O4, Na2Ti6O13 nanotubes, ZnO, γ-Al2O3, WO3, CeO2, and Ce0.5Zr0.5O2 supports. The CeO2 supported RuOx had the highest activity, and selectivity toward acetic acid, of all the materials when normalized with respect to Ru-loading. This high activity was independent of the surface area of the support and the loading of RuOx under the tested conditions. This was attributed to the highly uniform size of the RuOx deposits, demonstrating that the deposition is suitable for producing small nanoparticles at high loadings. To elucidate the reason for the promotional effect of CeO2, Ce0.5Zr0.5O2 was investigated as a high oxygen storage capacity support, however, this did not result in higher catalytic activity. The high activity of CeO2 supports compared to the low activity ZnO appear correlated to the presence of high valence Ru(VI) species analogous to that observed in literature.

Investigations of surface VOx species and their contributions to activities of VOx/Ti0.5Sn0.5O2 catalysts toward selective catalytic reduction of NO by NH3

High surface area Ti0.5Sn0.5O2 mixed oxide with rutile phase was prepared by a coprecipitation method. The surface area of Ti0.5Sn0.5O2 sample is 76.7m2g−1, and VOx/Ti0.5Sn0.5O2 catalysts were prepared using the mixed oxide as support. Characterizations using XRD, FT-IR, LRS, EPR, UV–vis, and TEM demonstrated that vanadium oxide species are highly dispersed on the surface of Ti0.5Sn0.5O2 support when the loading amount of vanadium oxide is ≤1.5mmolV/100m2 Ti0.5Sn0.5O2. The dispersed vanadium oxide species form epitaxial-growth layer on the support. In situ FT-IR (NH3 adsorption), combined with NH3-TPD, indicate that the catalyst with vanadium loading amount of 1.5mmolV/100m2 Ti0.5Sn0.5O2, which equals to the dispersion capability, possesses a maximum amount of Brønsted acid sites. The 1.5V/Ti0.5Sn0.5O2 catalyst exhibits the best catalytic performance and good resistance to water vapor poison for the “NO+NH3+O2” reaction, indicating that surface dispersed polymeric vanadium oxide species are the primary active species. A possible reaction mechanism is proposed on the basis of in situ FT-IR results.

Preparation of Co/Ce0.5Zr0.5O2 catalysts and their catalytic performance in methane partial oxidation to produce synthesis gas

Porous Ce0.5Zr0.5O2 solid solution support was prepared by co-precipitation and then different contents of Co (10%, 20%, and 30 %) were loaded over the Ce0.5Zr0.5O2 support by impregnation; the Co/Ce0.5Zr0.5O2 catalysts obtained in this way were used in partial oxidation of methane (POM) to produce synthesis gas. The fresh catalysts were characterized by N2 physical sorption (BET), X-ray diffraction (XRD), temperature-programmed reduction by hydrogen (H2-TPR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The amount of deposited carbon over the spent catalysts after POM tests was determined by temperature-programmed oxidation (O2-TPO) and thermogravimetric (TG) analysis. The results showed that cobalt oxide over Ce0.5Zr0.5O2 is easy to be reduced to metal cobalt. The Co/Ce0.5Zr0.5O2 catalysts show high activity and selectivity to H2 and CO in methane partial oxidation; higher Co loading is beneficial to enhance their catalytic activity and resistance to catalyst deactivation from coke deposition.

Low-temperature conversion of phenol into CO, CO2 and H2 by steam reforming over La-containing supported Rh catalysts

The steam reforming of phenol in the low-temperature range of 350–550°C was studied over 0.5wt% Rh supported on Ce0.15Zr0.85O2, Zr0.93La0.07O2, and Ce0.13Zr0.83La0.04O2 mixed metal oxides. The reforming specific activity (per gram of catalyst basis) was found to depend on (a) Rh dispersion, (b) the concentration (μmolg−1) of labile oxygen species of support, as determined by “oxygen storage capacity” measurements, and (c) the promotion of the water–gas shift (WGS) reaction rate, all of which largely influenced by the support chemical composition. The addition of 4atom% La3+ into the Ce0.15Zr0.85O2 crystal structure was found to largely promote the dispersion of Rh, to increase significantly (by a factor of 1.75) the concentration of surface basic sites (μmolm−2) of Ce0.13Zr0.83La0.04O2 compared to Ce0.15Zr0.85O2 support, to prevent to a large extent the inhibiting role of hydrogen in the rate of WGS reaction, and to influence significantly the concentration and structure of surface reaction intermediates of the WGS, namely: formate (HCOO–) and –OH groups formed on the support, and adsorbed CO formed on the Rh metal. The 0.5wt% Rh/Ce0.13Zr0.83La0.04O2 catalyst led to a significantly better performance towards steam reforming of phenol in terms of phenol conversion, H2-yield, and CO/CO2 product ratio in the 350–450°C range compared to a commercial Ni-based catalyst (44wt% Ni) used for steam reforming reactions. At 400°C, the 0.5wt% Rh/Ce0.13Zr0.83La0.04O2 catalyst exhibited approximately 54% and 50%, respectively, higher phenol conversion and hydrogen yield, compared to the Ni-based industrial catalyst. The significantly lower CO/CO2 product ratio obtained in the case of Rh/Ce0.13Zr0.83La0.04O2 compared to that obtained in the other supported-Rh catalysts is in agreement with the higher kinetic rate for the WGS reaction observed in the former catalyst.

One-step synthesis of ternary nanostructured CuO/Ti0.8Ce0.2O2 catalysts for low temperature CO oxidation

Ternary nanostructured CuO/Ti0.8Ce0.2O2 catalysts were prepared by a one-step surfactant-assisted method of nanoparticle assembly. The textural and structural properties of the CuO/Ti0.8Ce0.2O2 catalysts were characterized by XRD, TGA, BET, XPS and H2-TPR. Their catalytic performance for low-temperature CO oxidation was studied by using a catlab system. CuO supported on binary Ti0.8Ce0.2O2 support showed higher catalytic activity than CuO supported on single CeO2 or TiO2 support. The calcination temperature had a remarkable influence on the catalytic activity of the CuO/Ti0.8Ce0.2O2 catalysts. The CuO/Ti0.8Ce0.2O2 catalyst calcined at 500 °C exhibited the highest catalytic activity with T50% and T100% at 82 and 123 °C, respectively. According to the XRD, BET and H2-TPR analyses, the higher surface areas and more highly dispersed small particle size CuO should be responsible for the high catalytic activity of catalysts.