ZrO2-supported Catalysts Research Articles

Isotopic Tracer Studies of Reaction Pathways for Propane Oxidative Dehydrogenation on Molybdenum Oxide Catalysts

Kinetic analysis and isotopic tracer studies were used to identify the elementary steps and their reversibility in the oxidative dehydrogenation of propane over ZrO2-supported MoOx catalysts. Competitive reactions of C3H6 and CH313CH2CH3 showed that propene is the most abundant primary product, and that CO and CO2 are formed via either secondary combustion of propene, or by direct combustion of propane. A mixture of C3H8 and C3D8 undergoes oxidative dehydrogenation without forming C3H8-xDx mixed isotopomers, suggesting that steps involving C−H bond activation are irreversible. Normal kinetic isotopic effects (kC-H/kC-D) were measured for propane dehydrogenation (2.3), propane combustion (1.6) and propene combustion (2.1). These data indicate that the kinetically relevant steps in propane dehydrogenation and propene combustion involve the dissociation of C−H bonds in the respective reactant. H−D exchange occurs readily between C3H6 and D2O or C3D6 and H2O, suggesting that OH recombination steps are reversi...

Catalytic Oxidation of Methane over ZrO2-Supported Pd Catalysts

The catalytic oxidation of methane has been examined in an integral reactor over Pd/ZrO2catalysts in this study in order to determine how various preparation pretreatment and reaction variables influence activity. The conversion of methane versus temperature data indicate that mild oxidative and reductive treatments enhance the activity of a 5 wt% Pd/ZrO2catalyst while a higher-temperature reductive pretreatment produces a less efficient catalyst. Increasing the Pd loading from 0.1 to 10 wt% improves catalytic performance while higher loadings yield negligible improvement. Decay studies were performed on a 5 wt% Pd/ZrO2catalyst and compared to those of an optimized Pd/Al2O3catalyst. Under the conditions used in this study, the activity of the Pd/ZrO2catalyst remains fairly constant over a 50-hr period while the Pd/Al2O3catalyst initially exhibits an increase in activity but then a decrease after approximately 16 hr. At 250°C the Pd/ZrO2converts 56% of the methane to CO2and H2O after approximately 45 hr while the Pd/Al2O3catalytically oxidizes only 32% of the methane under the same conditions. An optimized Pd/ZrO2catalyst achieves a methane conversion of 100% below 300°C, which is 40°C lower than that obtained using the optimized Pd/Al2O3catalyst.The 5 wt% Pd/ZrO2CH4-oxidation catalyst also was characterized using X-ray photoelectron spectroscopy before and during heating in vacuum at 180°C and after treatment in a 2 : 1 mixture of O2and CH4at 180°C and 100 Torr for 45 min. The near-surface region of the as-entered catalyst consists mostly of ZrO2and PdO along with some Pd metal. Some of the PdO is reduced to Pd metal at 180°C, which is near the onset temperature for methane oxidation, and the Pd signal is diminished probably due to agglomeration of the Pd. Exposure of the catalyst to a 100 Torr mixture of 2 : 1 O2and CH4at 180°C for 45 min results in the formation of adsorbed CHx, CO and CO=3and/or HCO−3species. These data suggest that the CH4hydrogen bonds are first broken to form an adsorbed carbon species, which reacts with surface oxygen to form an adsorbed CO. This CO then reacts to form a surface carbonate or bicarbonate species which decomposes to form CO2.

Partial oxidation of methanol over supported palladium catalysts

Hydrogen production by partial oxidation of methanol (CH 3OH+1/2 O 2 ⇄2 H 2+CO 2) was studied over ZnO- and ZrO 2-supported Pd catalysts. Catalyst performance was investigated under feed ratios O 2/CH 3OH (molar) of 0.3 and 0.5 at 503–543 K. Irrespective of the large difference in BET area of Pd/ZnO and Pd/ZrO 2 catalysts, significant differences were observed when comparing H 2 selectivities. For the 1% Pd/ZnO catalyst, reaction occurs through consecutive oxidation → reforming steps. However, the behavior of catalyst 1% Pd/ZrO 2 approached that expected for Group 8 metals, that is, although the oxidation products are observed as for the catalyst 1% Pd/ZnO, the decomposition reaction seems to occur to a greater extent. Catalyst characterization by TPR, X-ray diffraction and XPS revealed that PdZn alloys can be formed upon reduction of Pd/ZnO catalysts at moderate temperatures.

Monolayer dispersion of oxides and salts on surface of ZrO2 and its application in preparation of ZrO2-supported catalysts with high surface areas

The thermostability of ZrO2 can be improved by dispersing a layer of an active component onto its surface in advance. The research results of seven kinds of catalysts (ZrO2-supported MoO3, WO3, CuO, SO4 2-, NiO, FeSO4 and Fe2O3) show that the surface areas of the samples prepared by impregnating Zr(OH)4 with the active components and then calcining at high temperature are much larger than those of the samples prepared with an ordinary method, namely, impregnating ZrO2 calcined at high temperature. The surface areas of the ZrO2-supported catalysts obtained in this way are several times that of pure ZrO2 calcined at the same temperature. The characteristic results show: (1) the active components are dispersed on the surface of ZrO2 as monolayer; (2) there is a good corresponding relationship between the surface coverage and the surface area of the sample; (3) as the loading of an active component comes up to its utmost dispersion capacity, the surface area of the sample will be the largest. The mechanism responsible for these phenomena has been discussed.

Catalytic properties of nickel molybdenum sulphide supported on zirconia

Zirconia has been investigated as a support material for Mo and NiMo sulphide catalysts. Thiophene HDS studies (1 atm, 400°C) reveal that the ZrO 2-supported Mo catalysts are twice as active as the corresponding Mo/Al 2O 3 catalysts. The promoting effect brought by nickel, however, is much smaller than expected in comparison with alumina supported catalysts; the use of zirconia induces higher hydrogenation selectivity. It is suggested that the promoter ions interact with both the Mo sulphide slab and the zirconia carrier, which results in a change in properties of the mixed catalytic sites. The increased selectivity towards hydrogenation may be an important advantage when dealing with hydrodenitrogenation processes. Indeed, in catalytic tests carried out at 70 atm, 350°C, 2,6-diethylaniline reacts more rapidly over zirconia catalysts ; similarly, the hydrogenation route is well developed in the complex reaction scheme of quinoline. However the inhibiting effect of quinoline (or 1,2,3,4-tetrahydroquinoline) upon the reactivity of alkylanilines is as strong on zirconia supported as on alumina supported catalysts. Nevertheless, the beneficial effect of the zirconia carrier is observed in the HDN of the less reactive phenanthridine molecule (140 atm, 340°C), and also in the HDN of real feed in a pilot test.

Hydrogenation of co over ZrO 2-supported Rh catalysts: kinetic aspects

To characterize the nature of the species present on a Rh/ZrO 2 catalyst during CO absorption, TPD and IR spectroscopic studies were conducted. The results have been used to satisfactorily account for the experimental rate equations determined for ethanol and methane formation by using CO and H 2 partial pressure dependence. The form of the rate expressions obtained for each product is explained in terms of a mechanism for the synthesis of both products.

Effect of Pd Dispersion on Methanol Decomposition over Supported Pd Catalysts

Abstract The turnover frequency (TF) for the methanol decomposition over various supported Pd catalysts is dependent upon both supporting materials and Pd crystallite sizes. On the other hand, the apparent activity (gas evolution rate per g-catalyst) is roughly proportional to the degree of Pd dispersion. This variation in the apparent activity is related to starting materials for the preparation of supports as well as to properties of supports. The highest dispersion of Pd was obtained with TiO2 prepared from Ti[OCH(CH3)2]4 or TiCl4, but at an elevated temperature (above 773 K) in the reduction treatment applied, it showed a suppressed activity. Pd particles on ZrO2 support gave a high value of TF when the Pd/ZrO2 catalyst was calcined in air at an elevated temperature (873–1073 K). The findings about the influence of heat treatment suggest that thermal stabilization of the ZrO2 support would play an important role in the development of catalytic properties of Pd. TF curves for the methanol decomposition over TiO2- and ZrO2-supported Pd catalysts change discontinously at about 10 Å of Pd particle size. In the case of Al2O3 support, characteristic behavior of TF curve are significantly different from those observed in the case of TiO2 and ZrO2 supports.

ChemInform Abstract: Hydrogenation of CO Over ZrO2‐Supported Rh Catalysts: Role of Experimental Parameters in Modifying the C2H5OH/CH4 Product Ratio.

ChemInformVolume 19, Issue 38 Preparative Organic Chemistry ChemInform Abstract: Hydrogenation of CO Over ZrO2-Supported Rh Catalysts: Role of Experimental Parameters in Modifying the C2H5OH/CH4 Product Ratio. C. MAZZOCCHIA, C. MAZZOCCHIA Dip. Chim. Ind. Ing. Chim., Politec. Milano, 20133 Milan, ItalySearch for more papers by this authorE. TEMPESTI, E. TEMPESTI Dip. Chim. Ind. Ing. Chim., Politec. Milano, 20133 Milan, ItalySearch for more papers by this authorP. GRONCHI, P. GRONCHI Dip. Chim. Ind. Ing. Chim., Politec. Milano, 20133 Milan, ItalySearch for more papers by this authorL. GIUFFRE, L. GIUFFRE Dip. Chim. Ind. Ing. Chim., Politec. Milano, 20133 Milan, ItalySearch for more papers by this authorL. ZANDERIGHI, L. ZANDERIGHI Dip. Chim. Ind. Ing. Chim., Politec. Milano, 20133 Milan, ItalySearch for more papers by this author C. MAZZOCCHIA, C. MAZZOCCHIA Dip. Chim. Ind. Ing. Chim., Politec. Milano, 20133 Milan, ItalySearch for more papers by this authorE. TEMPESTI, E. TEMPESTI Dip. Chim. Ind. Ing. Chim., Politec. Milano, 20133 Milan, ItalySearch for more papers by this authorP. GRONCHI, P. GRONCHI Dip. Chim. Ind. Ing. Chim., Politec. Milano, 20133 Milan, ItalySearch for more papers by this authorL. GIUFFRE, L. GIUFFRE Dip. Chim. Ind. Ing. Chim., Politec. Milano, 20133 Milan, ItalySearch for more papers by this authorL. ZANDERIGHI, L. ZANDERIGHI Dip. Chim. Ind. Ing. Chim., Politec. Milano, 20133 Milan, ItalySearch for more papers by this author First published: September 20, 1988 https://doi.org/10.1002/chin.198838082AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume19, Issue38September 20, 1988 RelatedInformation

Hydrogenation of CO over ZrO 2-supported Rh catalysts: Role of experimental parameters in modifying the [formula omitted] product ratio

The hydrogenation of CO over ZrO 2-supported rhodium catalyst has been extensively investigated in an attempt to increase the C 2 H 5 OH CH 4 ratio while minimizing CH 3OH. Only one scheme has been found to account satisfactorily for the experimental rate equation determined by using CO and H 2 partial pressure dependence. This scheme assumes the formation of a CH x moiety on the catalyst surface as the rate-determining step. Furthermore, in agreement with earlier findings, it is also consistent with the intermediate formation of acetaldehyde. Finally, the role of the support has been emphasized, as it has been found that ZrO 2 significantly affects ethanol selectivity.

Hydrodesulfurization over a TiO 2ZrO 2-supported CoOMoO 3 catalyst

The binary oxide TiO 2ZrO 2, whose chemical and physical properties were found to be strongly dependent on metal oxide ratio, precipitation methodology, and calcination temperature, was investigated as a support material for a CoOMoO 3 hydrodesulfurization (HDS) catalyst. Thiophene HDS studies at 1 atm and 300 °C revealed that the TiO 2ZrO 2-supported catalyst had an initial activity, on a weight basis, over twice that of a CoOMoO 3 Al 2O 3 catalyst, but suffered rapid deactivation. Nitric oxide chemisorption/temperature-programmed desorption (TPD) results suggest that the high initial activity of the TiO 2ZrO 2-supported catalyst may be due to a weaker Mo-support interaction, yielding a greater number of more reactive coordinatively unsaturated Mo sites. Thermal gravimetric analysis and differential scanning calorimetry results suggest that deactivation of the TiO 2ZrO 2-supported catalyst is at least in part due to coke formation.

Catalytic Activity of Highly Dispersed Palladium. II. X-Ray Photoelectron Spectroscopic and Thermal Desorption Studies of the Effects of ZrO2 Added to α-Alumina-supported Palladium

Abstract The effects of ZrO2 upon the catalytic properties of α-alumina-supported palladium for the hydrogenation of gaseous cyclohexene were studied by means of detailed kinetic analysis, thermal desorption (TD), and X-ray photoelectron spectroscopy (XPS). The catalysts, with ZrO2 added in amounts ranging from 0.1 to 45 in Zr/Pd ratio, were characterized by CO chemisorption and X-ray diffraction. The addition of ZrO2 at the Zr/Pd ratio of 0.5 enhanced the turn-over frequency of the hydrogenation by a factor of 7 and changed the hydrogen order of the reaction from 1.0 to 0.75 and the cyclohexene order from 0 to 0.6. The reaction with D2 exhibited deuteriumdistribution patterns similar to those for the reaction on the ZrO2-supported Pd catalysts. The hydrogenation pathway on the ZrO2-added catalyst was described by an associative mechanism in which the slow step was a surface reaction between a cyclohexyl radical and a hydrogen atom. In the thermal desorption spectra, the addition of ZrO2 caused a broadening of the adsorbed hydrogen peak as well as a shift of the dissolved hydrogen peak toward a lower temperature. The desorption of cyclohexene from Pd/α-Al2O3 catalysts underwent a disproportionation to produce benzene around 318 K and cyclohexane at 368 K, whereas the latter peak shifted by 70 K to the lowertemperature side upon the addition of ZrO2. The XPS study showed that the presence of ZrO2 provided Pd metal atoms in a negatively-charged state. The support effect was discussed on the basis of the interaction between Pd metal atoms and ZrO2 oxide.