The effect of Ce doping and pretreatment of Pt/Al2O3 on its catalysis of propane oxidation was investigated after aging the catalysts. The Ce amount and pretreatment conditions were varied, and the propane oxidation activity was measured. The properties of the catalysts were investigated by means of XRD, STEM-EDX, FT-IR, and H2-TPR. The size of the Pt nanoparticles (PtNPs) decreased for water-treated catalysts doped with a small amount of Ce, suggesting that water treatment of Ce-doped catalysts inhibits Pt sintering. The minimum PtNP size was obtained with ca. 3.6 wt% of Ce. The Ce species with less than 3.6 wt% existed in a dispersed state, whereas above this value, CeO2 particulates co-existed. The propane oxidation temperature of the water-treated catalysts was lowered to an extent that depended on the Ce content. This tendency is consistent with the PtNP size in the catalysts. It is considered that highly dispersed Ce species take a primary role in promoting propane oxidation on PtNPs. The reduction temperature of Ce species on water-treated catalysts was lower than that of untreated catalysts, probably owing to a stronger interaction between Pt and Ce, demonstrated by FT-IR measurements. The increased reducibility of Ce species may be the reason for the improved oxidation activity of the catalysts.
We prepared Pt catalysts supported on various metal oxides, viz., ZrO2, CeO2, TiO2, yttria-stabilized zirconia (YSZ), SiO2, SiO2–Al2O3, and γ-Al2O3, using an incipient wetness method and applied them to propane combustion. In the cases of ZrO2-, CeO2-, and TiO2-supported Pt catalysts, supports with different surface areas were also used. The Pt dispersion in Pt catalysts supported
on metal oxides increased with increasing surface area of the support for the same metal oxide. Pt catalysts on supports with
lower surface areas (ZrO2, CeO2, and TiO2) showed higher catalytic activities for propane combustion than did Pt catalysts on supports with higher surface areas. The
catalytic activity decreased in the following order: Pt/ZrO2 (2) > Pt/CeO2 (9) > Pt/TiO2 (1) = Pt/SiO2 (350) > Pt/ZrO2 (18) = Pt/YSZ > Pt/TiO2 (330) > Pt/SiO2–Al2O3 (350) > Pt/ZrO2 (73) > Pt/γ-Al2O3 (180) > Pt/CeO2 (160). The catalytic activity is inversely proportional to the amount of O2 chemisorbed up to the reaction temperature. It can be concluded that metallic Pt is essential for propane combustion and
is maintained for the Pt catalysts with large Pt metal particles, which can be prepared by using a support with a low surface
area. 相似文献
This study investigated the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with hydrocarbon in the presence of excess oxygen using various composition ratios of Pt/Al2O3, Rh/Al2O3 catalyst mixtures. The composition ratios were 1:1, 1:2, 2:1, 1:3 and 3:1 of 1 wt% Pt/Al2O3 and Rh/Al2O3, which are known to exhibit efficient NOx reduction at low and high temperatures among the noble metal catalysts. Experiments conducted on a single reductant revealed that more efficient NOx conversion could be obtained when Pt/Al2O3 and Rh/Al2O3 were mixed at a ratio of 3:1, rather than 1:1 or 1:3. In a single reductant condition, C3H6 800 ppm (2400 ppmC1) and 400 ppm (1200 ppmC1) exhibited 50% and 38% NOx conversion efficiency at 200°C, respectively. However, NOx conversion efficiency gradually decreased when temperatures were increased above 250°C. With regard to Pt/Al2O3 and Rh/Al2O3 ratio, higher ratios of Rh/Al2O3 activated this Pt+Rh/Al2O3 catalyst in the high temperature range. 相似文献
Supported vanadium oxides are one of the most promising alternative catalysts for propane dehydrogenation (PDH) and efforts have been made to improve its catalytic performance. However, unlike Pt‐based catalysts, the nature of the active site and surface structure of the supported vanadium catalysts under reductive reaction conditions still remain elusive. This paper describes the surface structure and the important role of surface‐bound hydroxyl groups on VOx / γ‐Al2O3 catalysts under reaction conditions employing in situ DRIFTS experiments and DFT calculations. It is shown that hydroxyl groups on the VOx /Al2O3 catalyst (V?OH) are produced under H2 pre‐reduction, and the catalytic performance for PDH is closely connected to the concentration of V?OH species on the catalyst. The hydroxyl groups are found to improve the catalyst that leads to better stability by suppressing the coke deposition. 相似文献
Pt‐Co/Al2O2 catalyst has been studied for CO2 reforming of CH4 to synthesis gas. It was found that the catalytic performance of me catalyst was sensitive to calcination temperature. When Co/Al2O3 was calcined at 1473 K prior to adding a small amount of Pt to it, the resulting bimetallic catalyst showed high activity, optimal stability and excellent resistance to carbon deposition, which was more effective to the reaction than Co/Al2O3 and Pt/Al2O3 catalysts. At lower metal loading, catalyst activity decreased in the following order: Pt‐Co/ Al2O3 > Pt/Al2O3 > Co/Al2O3. With 9% Co, the Co/Al2O3 calcined at 923 K was also active for CO2 reforming of CH4, however, its carbon formation was much more fast man that of the Pt‐Co/Al2O3 catalyst. The XRD results indicated that Pt species well dispersed over the bimetallic catalyst. Its high dispersion was related to the presence of CoAl2O4, formed during calcining of Co/Al2O3 at high temperature before Pt addition. Promoted by Pt, Co/Al2O4 in the catalyst could be reduced partially even at 923 K, the temperature of pre‐reduction for the reaction, confirmed by TPR. Based on these results, it was considered that the zerovalent platinum with high dispersion over the catalyst surface and the zerovalent cobalt resulting from Co/Al2O4 reduction are responsible for high activity of the Pt‐Co/Al2O3 catalyst, and the remain Co/Al2O4 is beneficial to suppression of carbon deposition over the catalyst. 相似文献
As a result of investigating low temperature isomerization of n-hexane at 130, 140, 150, 160°C in a flow reactor with a fixed bed of catalyst of the Al2O3/ZrO2/SO4/Pt type a ratio of components in the catalyst system was selected and process conditions were defined, which allow to obtain highly branched high-octane isomers with a yield of up to 40% relative to a transformed raw material. A kinetic model of the process was proposed and kinetic parameters were calculated. 相似文献
In heterogeneous catalysis, supports play a crucial role in modulating the geometric and electronic structure of the active metal phase for optimizing the catalytic performance. A γ‐Al2O3 nanosheet that contains 27 % pentacoordinate Al3+ sites can nicely disperse and stabilize raft‐like Pt‐Sn clusters as a result of strong interactions between metal and support. Consequently, there are strong electronic interactions between the Pt and Sn atoms, resulting in an increase in the electron density of the Pt sites. When used in the propane dehydrogenation reaction, this catalyst displayed an excellent specific activity for propylene formation with >99 % selectivity, and superior anti‐coking and anti‐sintering properties. Its exceptional ability to maintain the high activity and stability at ultrahigh space velocities further showed that the sheet construction of the catalyst facilitated the kinetic transfer process. 相似文献
Under the conditions of a joint reaction of propane and n-heptane at temperatures of 460–520°C and a pressure of 0.35 MPa, the conversion of propane and the concentration of C7+ aromatization products on platinum-containing catalysts modified by Group III (Ga) and Group IV (Ge, Ti, and Zr) elements were higher than those on an unmodified Pt/Al2O3 sample. This is explained by a change in the aprotic acidity of the catalysts as a result of the support modification. The sample with the addition of gallium was most active. A plausible reason for this is the conversion of hydrocarbons at active sites that consist of Pt and Ga, which were formed upon catalyst activation. It is believed that gallium adjacent to platinum in an ionic form on the support surface acts as an aprotic acid site. 相似文献
The decomposition of natural gas over Pd-NiO/Al2O3 and Pt-Sn/Al2O3 is carried out in a microwave catalytic reaction at room temperature. The decomposition of methane is caused by collision by excitation of unstable electronic state. Measuring the flow rate and plasma power can provide kinetic data and indicate the mechanism. The conversion of C2 products increases from 47 to 63.7% in the microwave plasma catalytic reaction with electric field. Comparing the activities of catalysts, Pd-NiO/Al2O3 bimetallic catalyst is more active than Pt-Sn/Al2O3 catalyst because of modification of the surface of catalysts by carbon formation. The kinetic modeling of plasma of methane conversion seems related to the power of the electric discharge. It was also revealed that proper coking or polymeric carbon formation improves the catalytic activity; therefore, the conversion of methane may increase over Pd-Ni/Al2O3 catalyst in the plasma system. 相似文献
Heptene-2 aromatization on Pt/Al2O3 in a pulse microcatalytic reactor has been studied under H2 and N2 atmosphere at temperatures between 330 to 500°C and at a total pressure of 4.0 kg/cm2. Results showed that the production of only cracked products (mainly methane) from deep fragmentation of heptene-2 in H2 sharply contrasts with the reaction in N2 in which the catalyst showed aromatic selectivity with the production of methane, benzene and toluene. In H2-N2 mixtures, 75% H2 was required to reduce the aromatization activity of the catalyst to zero. A test of the kinetic data using Sica's method [15] of pulse kinetic analysis suggests a first order in heptene-2 with an activation energy of 102.61 kJ/mol in N2 and 124.71 kJ/mol in H2. The difference in activation energies has been attributed to a difference in reaction mechanisms in both gases. 相似文献
The interactions of Al2O3, CeO2, Pt/Al2O3, and Pt/CeO2 films with SO2, SO2 + H2O, SO2 + O2, and SO2 + O2 + H2O in the temperature range 300–673 K at the partial pressures of SO2, O2, and H2O equal to 1.5 × 102, 1.5 × 102, and 3 × 102 Pa, respectively, were studied using X-ray photoelectron spectroscopy. The formation of surface sulfite at T 473 K (the S 2p3/2 binding energy (Eb) is 167.5 eV) and surface sulfate at T 573 K (Eb = 169.2 eV) was observed in the reactions of Al2O3 and CeO2 with SO2. The formation of sulfates on the surface of CeO2 occurred much more effectively than in the case of Al2O3, and it was accompanied by the reduction of Ce(IV) to Ce(III). The formation of aluminum and cerium sulfates and sulfites on model Pt/Al2O3 and Pt/CeO2 catalysts occurred simultaneously with the formation of surface platinum sulfides (Eb of S 2p3/2 is 162.2 eV). The effects of oxygen and water vapor on the nature and yield of sulfur-containing products were studied. 相似文献
Novel γ-Al2O3 supported nickel (Ni/Al2O3) catalyst was developed as a functional layer for Ni–ScSZ cermet anode operating on methane fuel. Catalytic tests demonstrated Ni/Al2O3 had high and comparable activity to Ru–CeO2 and much higher activity than the Ni–ScSZ cermet anode for partial oxidation, steam and CO2 reforming of methane to syngas between 750 and 850 °C. By adopting Ni/Al2O3 as a catalyst layer, the fuel cell demonstrated a peak power density of 382 mW cm?2 at 850 °C, more than two times that without the catalyst layer. The Ni/Al2O3 also functioned as a diffusion barrier layer to reduce the methane concentration within the anode; consequently, the operation stability was also greatly improved without coke deposition. 相似文献
Mechanism of Sintering of Highly Dispersed Pt on Al2O3 in Oxygen Sintering of highly dispersed Pt on alumina in O2 consists in a slow thermal decomposition of a PtIV surface compound, followed by a fast coalescence of the highly mobile, zerovalent Pt, formed during the decomposition. Sintering according to this mechanism is inhibited by O2. The slower Ostwald ripening, promoted by O2, comes into effect only after complete decomposition of the PtIV surface compound. 相似文献
By means of density functional theory computations, we examine the stability and CO oxidation activity of single Ru on CeO2(111), TiO2(110) and Al2O3(001) surfaces. The heterogeneous system Ru1/CeO2 has very high stability, as indicated by the strong binding energies and high diffusion barriers of a single Ru atom on the ceria support, while the Ru atom is rather mobile on TiO2(110) and Al2O3(001) surfaces and tends to form clusters, excluding these systems from having a high efficiency per Ru atom. The Ru1/CeO2 exhibits good catalytic activity for CO oxidation via the Langmuir–Hinshelwood mechanism, thus is a promising single‐atom catalyst. 相似文献
An effective method was developed for preparing highly dispersed CeO2 nanoparticle on a Pt/C catalyst synthesized by a continuous two-step process. From the XRD patterns, the diffraction pattern of the 20Pt–10CeO2/C catalyst revealed that both crystalline Pt and CeO2 phases coexisted. The TEM images show that the Pt and CeO2 nanoparticles were well-dispersed on the surface of the carbon support, which is known to be important for activity in the ORR test. In the ORR and single-cell tests, the 20Pt–10CeO2/C catalyst showed higher performance than a commercial 20Pt/C catalyst, owing to the oxygen storage capacity of CeO2 and its ability to rapidly exchange oxygen with oxygen in the buffer. 相似文献
Transformations of Pt/TiO2 catalyst between non-SMSI and SMSI states have been investigated by repeatedH2–O2 titration. The decline of capacity of H2 and O2 chemisorption and their reaction on Pt particles is accountable by reduction of superficial labile oxygen species in the temperature range of 298–573 K and an increase of surface oxygen vacancies on TiO2 above 573 K, respectively. 相似文献