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1.
A catalytic study of the hydrogen production by CO water gas shift reaction (WGSR) on gold, silver and copper particles supported on TiO 2 has been carried out. A deep characterisation of the catalysts by TPR and FTIR has been performed. Silver catalyst exhibits no catalytic activity, copper and gold catalysts show intermediate and very high performances, respectively. These strong differences have been interpreted on the basis of FTIR data of CO adsorption at 90 K and on the effect of coadsorbed species. Gold and copper catalysts, either oxidised or reduced, are able to adsorb CO. Reduced silver catalyst does not adsorb CO at all, while oxidised silver catalyst does quite strongly. 相似文献
2.
Gold and palladium were supported on a mesoporous TiO 2 for total oxidation of volatile organic compounds (VOCs). Mesoporous high surface area titania support was synthesised using of Ti(OC 2H 5) 2 in the presence of CTMABr surfactant. After removing the surfactant molecules, 0.5 or 1.5 wt% of palladium and 1 wt% of gold were precipitated on the support by, respectively, wet impregnation and deposition–precipitation methods. The activity for toluene and propene total oxidation of the prereduced samples follows the same order: 0.5%Pd-1%Au/TiO 2 > 1.5%Pd/TiO 2 > 0.5%Pd/TiO 2 > 1%Au-0.5%Pd/TiO 2 > 1%Au/TiO 2 > TiO 2. Moreover, a catalytic comparison with samples based on a conventional TiO 2, shows the catalytic advantage of the mesoporous TiO 2 support. The promotional effect of gold added to palladium could be partly explained by small metallic particles (TEM), but meanly by metallic particles made up of Au-rich core with a Pd-rich shell. Moreover, the hydrogen TPR profile of 0.5%Pd-1%Au/TiO 2 shows only the signal attributed to small PdO particles. Gold also implies a protecting effect of the support under reduction atmosphere. Operando diffuse reflectance infrared fourier transform (DRIFT) spectroscopy was carried on and allowed to follow the VOCs oxidation and the formation of coke molecules, but also a metallic electrodonor effect to the adsorbed molecule which increases in the same order as the activity for oxidation reaction. The presence of coke after test was also shown by DTA–TGA by exothermic signals between 300 and 500 °C and by EPR ( g = 2.003). 相似文献
3.
Mesoporous ZrO 2 with high surface area and uniform pore size distribution, synthesized by surfactant templating through a neutral [C 13(EO) 6–Zr(OC 3H 7) 4] assembly pathway, was used as a support of gold catalysts prepared by deposition–precipitation method. The supports and the catalysts were characterized by powder X-ray diffraction, scanning and transmission electron microscopy, N 2 adsorption analysis, temperature programmed reduction and desorption. The catalytic activity of gold supported on mesoporous zirconia was evaluated in water–gas shift (WGS) reaction at wide temperature range (140–300 °C) and at different space velocities and H 2O/CO ratios. The catalytic behaviour and the reasons for а reversible deactivation of Au/mesoporous zirconia catalysts were studied. The influence of gold content and particle size on the catalytic performance was investigated. The WGS activity of the new Au/mesoporous zirconia catalyst was compared to the reference Au/TiO 2 type A (World Gold Council), revealing significantly higher catalytic activity of Au/mesoporous zirconia catalyst. It is found that the mesoporous zirconia is a very efficient support of gold-based catalyst for the WGS reaction. 相似文献
4.
Supported gold catalysts derived from interaction of a Au–phosphine complex Au(PPh 3)(NO 3) (1) with conventional titanium oxide TiO 2 and as-precipitated titanium hydroxide
(*, as-precipitated) have been characterized by means of XRD, XPS, EXAFS, and
CP/MAS–NMR. The Au complex 1 was supported on TiO 2 and
without loss of Au–P bonding at room temperature. The Au complex 1 on TiO 2 was readily and completely decomposed to form metallic gold particles by calcination at 473 K, whereas only a small part of the complex 1 on
was transformed to metallic gold particles. By calcination of 1/
at 573 K the formation of both metallic gold particles and crystalline titanium oxides became notable as evidenced by XRD, XPS and
CP/MAS–NMR. The mean diameter of Au particles in 1/
calcined at 673 K was less than 30 Å as estimated from Au(2 0 0) diffraction, which was about one-tenth of that for the corresponding 1/TiO 2. Thus the as-precipitated titanium hydroxide
was able to stabilize the Au complex 1 to lead to the simultaneous decomposition of Au complex and
. The catalyst 1/
calcined at 673 K afforded remarkably high catalytic activity for low-temperature CO oxidation at 273–373 K as compared to the catalyst 1/TiO 2. 相似文献
5.
The oxidation of perchloroethylene (PCE) was investigated over chromium oxide catalysts supported on SiO 2, SiO 2–Al 2O 3, activated carbon, mordenite type zeolites, MgO, TiO 2 and Al 2O 3. Supported chromium oxide catalysts were more active than any other metal oxide catalysts including noble metal examined in the present study. PCE removal activity of chromium oxide catalysts mainly depended on the type of supports and the content of metal loaded on the catalyst surface. TiO 2 and Al 2O 3 containing high surface areas were effective for the high performance of PCE removal, since the formation of well dispersed Cr(VI) active reaction sites for the present reaction system, was enhanced even for the high Cr loading on the catalyst surface. CrO x catalysts supported on TiO 2 and Al 2O 3 also exhibited stable PCE removal activity at a low feed concentration of PCE of 30 ppm up to 100 h at 350°C. However, significant catalyst deactivation was observed at high PCE concentration of 10 000 ppm. CrO x/TiO 2 revealed stronger water tolerance than CrO x/Al 2O 3 due to the surface hydrophobicity. 相似文献
6.
The catalytic activities of Pt and Au supported on TiO 2 were compared with respect to the oxidation of CO and propane. While the Au catalysts showed higher activities for CO oxidation, the Pt catalysts were more active for propane combustion. A strong de-activation of the CO oxidation activity by SO 2 was observed only over the TiO 2-supported Au catalyst, indicating that SO 2 can block the active sites for CO oxidation over Au catalysts. The results are consistent with a model in which the perimeter sites have a special role in the CO oxidation reaction over Au catalysts. 相似文献
7.
Gravimetric temperature programmed oxidation was used to study the combustion of a diesel soot mixed with copper catalysts supported on La 2O 3 or La 2O 2CO 3. In a first step, different systems associating copper oxide with an other metal oxide were prepared and tested in presence of SO 2. The association of copper and niobium was found the most active. The influence of alkali on the activity was also studied. It results that potassium is the most effective in lowering the combustion temperature domain in agreement with literature. Finally, Cu---Nb---K catalysts deposited on lanthanum oxide have an improved catalytic activity at low temperatures compared to Cu---V---K or Cu---Mo---K/TiO 2, reported in literature. For this catalyst, the maximum oxidation rate was observed at ca. 300°C with the combustion starting at about 250°C. A similar behaviour is obtained when replacing Nb by Ta or the support La 2O 3 by either La 2O 2CO 3 or TiO 2. 相似文献
8.
The conversion of C3 organic compounds (propane, propene, 1- and 2-propanol, allyl alcohol, propanal, acrolein, acetone and 1- and 2-chloropropane) in the presence of excess oxygen has been investigated over two V–W–TiO 2 commercial SCR catalysts differing in the V content and over Mn–TiO 2 alternative SCR catalysts. V–W–Ti catalysts show poor activity in the oxidation of hydrocarbons and oxygenates and give significant amounts of partial oxidation products. Moreover they give rise to CO in excess of CO 2. The sample higher in V is more active. Mn–TiO 2 is definitely more active in oxidation of hydrocarbons and oxygenates, and produces, at total conversion, CO 2 as the only detectable product. V–W–Ti catalysts are very active in dehydrochlorination of the two 2-chloropropane isomers and retain the same oxidation activity also in the presence of HCl. On the contrary, Mn-based catalysts in the presence of chlorocarbons convert into dehydrochlorination catalysts but lose their catalytic activity in oxidation. V–W–Ti catalysts can be used in Cl-containing atmospheres while Mn–TiO2 can be proposed for DeNOx and VOC abatement in Cl-free atmospheres such as for diesel engine exhaust gas purification. 相似文献
9.
The TiO 2 supported noble metal (Au, Rh, Pd and Pt) catalysts were prepared by impregnation method and characterized by means of X-ray diffraction (XRD) and BET. These catalysts were tested for the catalytic oxidation of formaldehyde (HCHO). It was found that the order of activity was Pt/TiO 2 Rh/TiO 2 > Pd/TiO 2 > Au/TiO 2 TiO 2. HCHO could be completely oxidized into CO 2 and H 2O over Pt/TiO 2 in a gas hourly space velocity (GHSV) of 50,000 h −1 even at room temperature. In contrast, the other catalysts were much less effective for HCHO oxidation at the same reaction conditions. HCHO conversion to CO 2 was only 20% over the Rh/TiO 2 at 20 °C. The Pd/TiO 2 and Au/TiO 2 showed no activities for HCHO oxidation at 20 °C. The different activities of the noble metals for HCHO oxidation were studied with respect to the behavior of adsorbed species on the catalysts surface at room temperature using in situ DRIFTS. The results show that the activities of the TiO 2 supported Pt, Rh, Pd and Au catalysts for HCHO oxidation are closely related to their capacities for the formation of formate species and the formate decomposition into CO species. Based on in situ DRIFTS studies, a simplified reaction scheme of HCHO oxidation was also proposed. 相似文献
10.
The water-gas shift (WGS) activity of platinum catalysts dispersed on a variety of single metal oxides as well as on composite MO x/Al 2O 3 and MO x/TiO 2 supports (M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, La, Ce, Nd, Sm, Eu, Gd, Ho, Er, Tm) has been investigated in the temperature range of 150–500 °C, using a feed composition consisting of 3% CO an 10% H 2O. For Pt catalysts supported on single metal oxides, it has been found that both the apparent activation energy of the reaction and the intrinsic rate depend strongly on the nature of the support. In particular, specific activity of Pt at 250 °C is 1–2 orders of magnitude higher when supported on “reducible” compared to “irreducible” metal oxides. For composite Pt/MO x/Al 2O 3 and Pt/MO x/TiO 2 catalysts, it is shown that the presence of MO x results in a shift of the CO conversion curve toward lower reaction temperatures, compared to that obtained for Pt/Al 2O 3 or Pt/TiO 2, respectively. The specific reaction rate is in most cases higher for composite catalysts and varies in a manner which depends on the nature, loading, and primary crystallite size of dispersed MO x. Results are explained by considering that reducibility of small oxide particles increases with decreasing crystallite size, thereby resulting in enhanced WGS activity. Therefore, evidence is provided that the metal oxide support is directly involved in the WGS reaction mechanism and determines to a significant extent the catalytic performance of supported noble metal catalysts. Results of catalytic performance tests obtained under realistic feed composition, consisting of 3% CO, 10% H 2O, 20% H 2 and 6% CO 2, showed that certain composite Pt/MO x/Al 2O 3 and Pt/MO x/TiO 2 catalysts are promising candidates for the development of active WGS catalysts suitable for fuel cell applications. 相似文献
11.
Mo---Co or Mo---Ni catalysts supported on alumina (Al 2O 3) have been widely used for hydrodesulfurization (HDS) of heavy petroleum fractions. In order to enhance the catalytic activities for HDS, a composite type support (TiO 2-Al 2O 3) prepared by the chemical vapor deposition (CVD) method has been studied. We found that Mo catalyst supported on TiO 2-Al 2O 3 showed much higher catalytic activity for HDS of dibenzothiophene derivatives than the catalysts supported on Al 2O 3. 相似文献
12.
New gold catalytic system prepared on ceria-modified mesoporous titania (CeMTi) used as water-gas shift (WGS) reaction catalyst is reported. Mesoporous titania (MTi) was synthesized using surfactant templating method through a neutral [C 13(EO) 6–Ti(OC 3H 7) 4] assembly pathway. Ceria modifying additive was deposited on MTi by deposition precipitation (DP) method. Gold-based catalysts with different gold content (1–5 wt.%) were synthesized by DP of gold hydroxide on mixed metal oxide support. The supports and the catalysts were characterized by powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N 2 adsorption analysis and temperature-programmed reduction (TPR). The catalytic behavior of the gold-based catalysts was evaluated in WGS reaction in a wide temperature range (140–300 °C) and at different space velocities and H 2O/CO ratios. The influence of gold content and particle size on the catalytic performance was investigated. The WGS activity of the new gold/ceria-modified mesoporous titania catalysts was compared with that of gold catalysts supported on simple oxides CeO 2 and mesoporous TiO 2, as well as gold/ceria-modified titania and reference catalyst Au/TiO 2 type A (World Gold Council). A high degree of synergistic interaction between ceria and mesoporous titania and a positive modification of structural and catalytic properties by ceria has been achieved. It is clearly revealed that the ceria-modified mesoporous titania is of much interest as potential support for gold-based catalyst. The Au/ceria-modified mesoporous titania catalytic system is found to be efficient catalyst for WGSR. 相似文献
13.
Au-based catalysts, known for ambient temperature CO oxidation, have to provide stable performance of up to 5000 h in order to be commercially applicable in automotive fuel cells. In this report, the on-line deactivation characteristics of Au/TiO 2 in unconventional PROX conditions are discussed. As opposed to CO removal from air, results in this report suggests that carbonates have a minor effect on deactivation of Au/TiO 2 in dry H 2-rich conditions. Also, no conclusive correlation between surface hydration and deactivation was observed. Rather, deactivation appeared to have occurred as a result of an intrinsic transformation in the oxidation state of the active species in the reducing operating conditions; a process which was reversible in an oxidizing atmosphere. 相似文献
14.
The influence of Lewis and Brønsted acid sites on the performance of V 2O 5/TiO 2 and V 2O 5–WO 3/TiO 2 catalysts in the total oxidation of o-dichlorobenzene was investigated. Catalytic activity of these materials resulted strongly affected by their acidic properties. The presence of Brønsted acid sites significantly increases the o-DCB conversion but also leads to the uncompleted degradation of chlorinated compounds, promoting the formation of partial oxidation products, as dichloromaleic anhydride. On the contrary, Lewis acid sites, acting as absorbing sites, promote the further oxidation of intermediates to CO and CO 2, without any by-products desorption. Furthermore, the presence of water in the feed-stream was proven to decrease o-DCB conversion but also to play a positive role on process selectivity, increasing COx production. Plausible reasons for this effect are the reduction of Brønsted acid sites and the hydrolysis of anhydride during wet tests. 相似文献
15.
The effect of the TiO 2–Al 2O 3 mixed oxide support composition on the hydrodesulfurization (HDS) of gasoil and the simultaneous HDS and hydrodenitrogenation (HDN) of gasoil+pyridine was studied over two series of CoMo and NiMo catalysts. The intrinsic activities for gasoil HDS and pyridine HDN were significantly increased by increasing the amount of TiO 2 into the support, and particularly over rich- and pure-TiO 2-based catalysts. It is suggested that the increase in activity be due to an improvement in reducing and sulfiding of molybdena over TiO 2. The inhibiting effect of pyridine on gasoil HDS was found to be similar for all the catalysts, i.e., was independent of the support composition. The ranking of the catalysts for the gasoil HDS test differed from that obtained for the thiophene test at different hydrogen pressures. In the case of gasoil HDS, the activity increases with TiO 2 content and large differences are observed between the catalysts supported on pure Al 2O 3 and pure TiO 2. In contrast, in the case of the thiophene test, the pure Al 2O 3-based catalyst appeared relatively more active than the catalysts supported on mixed oxides. Also, in the thiophene test the difference in intrinsic activity between the pure Al 2O 3-based catalyst appeared relatively more active than the catalysts supported on mixed oxides. Also in the thiophene test, the difference in intrinsic activity between the pure Al 2O 3- and pure TiO 2-based catalysts is relatively small and dependent on the H 2 pressure used. Such differences in activity trend among the gasoil and the thiophene tests are due to a different sensitivity of the catalysts (by different support or promoter) to the experimental conditions used. The results of the effect of the H 2 partial pressure on the thiophene HDS, and on the effect of H 2S concentration on gasoil HDS demonstrate the importance of these parameters, in addition to the nature of the reactant, to perform an adequate catalyst ranking. 相似文献
16.
The surface properties of a series of V 2O 5 catalysts supported on different oxides (Al 2O 3, H–Na/Y zeolite, MgO, SiO 2, TiO 2 and ZrO 2) were investigated by transmission electron microscopy and FTIR spectroscopy augmented by CO and NH 3 adsorption. In the case of the V 2O 5/SiO 2 system TEM images evidenced the presence of V 2O 5 crystallites, whereas such segregated phase was not observed for the other samples. VO x species resulted widely spread on the surface of Al 2O 3, H–Na/Y zeolite, MgO and SiO 2, whereas on TiO 2 and ZrO 2 they are assembled in a layer covering almost completely the support. Furthermore, evidences for the presence in this layer of V–OH Brønsted acid sites close to the active centres were found. It is proposed that propene molecules primarily produced by oxydehydrogenation of propane can be adsorbed on this acid centres and then undergo an overoxidation by reaction with redox centres in the neighbourhood. This features could account for the low selectivity of V 2O 5/TiO 2 and V 2O 5/ZrO 2 catalysts. 相似文献
17.
Gold loaded on TiO 2 (Au/TiO 2) catalysts were prepared using Au(I)–thiosulfate complex (Au(S 2O 3) 23−) as the gold precursor for the first time. The samples were characterized by UV–vis diffuse reflectance spectra, X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic absorption flame emission spectroscopy (AAS), and X-ray photoelectron spectroscopy (XPS) methods. Using Au(S 2O 3) 23− as gold precursor, ultra-fine gold nanoparticles with a highly disperse state can be successfully formed on the surface of TiO 2. The diameter of Au nanoparticles increases from 1.8 to 3.0 nm with increasing the nominal Au loading from 1% to 8%. The photocatalytic activity of Au/TiO 2 catalysts was evaluated from the analysis of the photodegradation of methyl orange (MO). With the similar Au loading, the catalysts prepared with Au(S 2O 3) 23− precursor exhibit higher photocatalytic activity for methyl orange degradation when compared with the Au/TiO 2 catalysts prepared with the methods of deposition–precipitation (DP) and impregnation (IMP). The preparation method has decisive influences on the morphology, size and number of Au nanoparticles loaded on the surface of TiO 2 and further affects the photocatalytic activity of the obtained catalysts. 相似文献
18.
The kinetics of CO oxidation and NO reduction reactions over alumina and alumina-ceria supported Pt, Rh and bimetallic Pt/Rh catalysts coated on metallic monoliths were investigated using the step response technique at atmospheric pressure and at temperatures 30–350°C. The feed step change experiments from an inert flow to a flow of a reagent (O 2, CO, NO and H 2) showed that the ceria promoted catalysts had higher adsorption capacities, higher reaction rates and promoting effects by preventing the inhibitory effects of reactants, than the alumina supported noble metal catalysts. The effect of ceria was explained with adsorbate spillover from the noble metal sites to ceria. The step change experiments CO/O 2 and O 2/CO also revealed the enhancing effect of ceria. The step change experiments NO/H 2 and H 2/NO gave nitrogen as a main reduction product and N 2O as a by-product. Preadsorption of NO on the catalyst surface decreased the catalyst activity in the reduction of NO with H 2. The CO oxidation transients were modeled with a mechanism which consistent of CO and O 2 adsorption and a surface reaction step. The NO reduction experiments with H 2 revealed the role of N 2O as a surface intermediate in the formation of N 2. The formation of NN bonding was assumed to take place prior to, partly prior to or totally following to the NO bond breakage. High NO coverage favors N 2O formation. Pt was shown to be more efficient than Rh for NO reduction by H 2. 相似文献
19.
Experiments determined methanol removal and catalyst elutriation rates during photocatalytic oxidation (PCO) of fluidized and packed beds of various titania-based catalysts. The study developed elutriation-resistant catalysts in which TiO 2 was precipitated from solution (p-TiO 2), or was coated on an Al 2O 3 support (TiO 2/Al 2O 3) and compared them to Degussa P-25 TiO 2. Although Degussa P-25 TiO 2 oxidized methanol effectively, it elutriated at a rate that was two orders of magnitude greater than those of p-TiO 2 and TiO 2/Al 2O 3. In addition, TiO 2/Al 2O 3 removed methanol at a significantly greater rate than did P-25, with p-TiO 2 being the least active. Fluidized beds produced greater PCO rates than did packed beds of P-25 and TiO 2/Al 2O 3. Fluidization enhancers, such as vibration and incorporation of a static mixer, improved the performance of the P-25 fluidized bed, but did not change the effectiveness of TiO 2/Al 2O 3 or p-TiO 2. The activity of TiO 2/Al 2O 3 decreased with increasing calcination temperature (over the temperature range 673–873 K). The optimum TiO 2 loading for TiO 2/Al 2O 3 was 30 wt.%. 相似文献
20.
The catalytic oxidation of sulfur dioxide to sulfur trioxide over several binary (M xO y/TiO 2) and ternary (V 2O 5/M XO Y/TiO 2) supported metal oxide catalysts was systematically investigated. The supported metal oxide components were essentially 100% dispersed as surface metal oxide species, as confirmed by Raman spectroscopy characterization. The sulfur dioxide oxidation turnover frequencies of the binary catalysts were all within an order of magnitude (V 2O 5/TiO 2>Fe 2O 3/TiO 2>Re 2O 7/TiO 2 CrO 3/TiO 2 Nb 2O 5/TiO 2>MoO 3/TiO 2 WO 3/TiO 2). An exception was the K 2O/TiO 2 catalysts, which is essentially inactive for sulfur dioxide oxidation. With the exception of K 2O, all of the surface metal oxide species present in the ternary catalysts (i.e., oxides of V, Fe, Re, Cr, Nb, Mo and W) can undergo redox cycles and oxidize SO 2 to SO 3. The turnover frequency for sulfur dioxide oxidation over all of these catalysts is approximately the same at both low and high surface coverages. This indicates that the mechanism of sulfur dioxide oxidation is not sensitive to the coordination of the surface metal oxide species. A comparison of the activities of the ternary catalysts with the corresponding binary catalysts suggests that the surface vanadium oxide and the additive surface metal oxide redox sites act independently without synergistic interactions. The V 2O 5/K 2O/TiO 2 catalyst showed a dramatic reduction in the catalytic activity in comparison to the unpromoted V 2O 5/TiO 2 catalyst. The ability of K 2O to significantly retard the redox potential of the surface vanadia species is primarily responsible for the lower catalytic activity of the ternary catalytic system. The fundamental insights generated from this research can potentially assist in the molecular design of the air pollution control catalysts: (1) the development of catalysts for low temperature oxidation of SO 2 to SO 3 during sulfuric acid manufacture (2) the design of efficient SCR DeNO x catalysts with minimal SO 2 oxidation activity and (3) improvements in additives for the simultaneous oxidation/sorption of sulfur oxides in petroleum refinery operations. 相似文献
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