ZrO2-supported Catalysts Research Articles

Single-stage medium temperature water-gas shift reaction over Pt/ZrO2 – Support structural polymorphism and catalyst deactivation

Influence of zirconia polymorphism on water-gas shift reaction was investigated. The study was carried out over catalysts with similar features, which allowed assessing any effect brought about by the support crystalline structure. It was found that zirconia polymorphism determines the catalyst activity and the monoclinic structure renders a more active system. It is most likely due to the presence of hydroxyl groups, which have been claimed to be involved in the formation of important reaction intermediates. Catalyst deactivation was also addressed and it could be concluded that the changes in metal phase dispersion along reaction play a quite important role on the ZrO2-supported catalyst stability.

Intramolecular selective hydrogenation of cinnamaldehyde over CeO2–ZrO2-supported Pt catalysts

Selective liquid phase hydrogenation of cinnamaldehyde is reported, for the first time, over CeO2, ZrO2, and CeO2–ZrO2-supported Pt catalysts. Cinnamyl alcohol is the selective product. These catalysts are highly active and selective even at 25°C and found to be superior to most of the hitherto known supported Pt catalysts. Alkali addition (NaOH) has enhanced the performance of these catalysts. At an optimized reaction condition, 95.8% conversion of cinnamaldehyde and 93.4% selectivity of cinnamyl alcohol have been obtained. Acidity of the support (due to the presence of ZrO2 component) and higher electron density at Pt (due to CeO2 component) are attributed to be responsible for the superior catalytic activity of Pt supported on CeO2–ZrO2 composite material.

Effect of the Calcination Temperature on the Catalyst Performance of ZrO<sub>2</sub>-Supported Cobalt for Fischer-Tropsch Synthesis

The effect of the calcination temperature on the catalyst performance of ZrO2-supported cobalt for Fischer-Tropsch synthesis is investigated. Results show that the size of the cobalt species particles of the ZrO2-supported cobalt catalysts increases and their reducibility is enhanced with increasing calcination temperature. In addition, the extent of CO linear absorption and bridge absorption peak increases and then decreases with increasing calcination temperature. The results from the Fishcer-Tropsch synthesis show that the CO conversion rate increases and then decreases as the calcination temperature is increased. Catalyst selectivity for C1 monotonically decreases, whereas that for C5+ increases. The changes in the CO conversion rate demonstrate a regularity consistent with the trend of the CO absorption peak extent. Meanwhile, the growth and enhanced reducibility of the cobalt species particles contribute to the generation of heavy hydrocarbons and explain the differences in product selectivity. Therefore, the appropriate calcination temperature facilitates an increase in the CO conversion rate of the ZrO2-supported cobalt catalysts and results in a better Fischer-Tropsch synthesis product selectivity.

Production of Di-isopropyl ether (DIPE) over 12-Molybdophosphoric Acid Supported on ZrO2. An Alternative Octane Enhancer for Lead-free Petrol

AbstractSolid acid catalysts of 12-Molybdophosphoric acid (MoP) supported on hydrous zirconia have been synthesized using impregnation method. Structural transformations due to thermal effects have been studied by different techniques including X-Ray diffraction, thermogravimetric analysis (TGA), infrared absorption (DRIFT), Raman spectroscopy and31P MAS NMR. These techniques showed that the heteropolyacid present undegradedKegginstructure. The transformation of heteropoly anion of pure HPMo to MoO3begins at a temperature lower than that for its ZrO2-supported counterpart. The activity of ZrO2-supported (MoP-Z) catalysts in the 2-propanol decomposition presents a high selectivity to the formation of DIPE and propene, this selectivity is related with acid sites determined by thermodesorption (TPD) of NH3.

Manganese-containing VOC oxidation catalysts prepared in molten salts

Mn-Zr and Mn-Ti supported oxide catalysts have been prepared by means of reactions in molten Na(K)NO 3 fluxes at 500 °C. The solids were characterized using X ray diffraction, textural measurements, optical spectroscopy and transmission electron microscopy. Highly dispersed ZrO 2 and TiO 2 covered with Mn(III, IV) species were obtained from the reaction in the melt. Due to the stabilizing effect of Mn, ZrO 2-based solids with specific surface areas up to 220 m 2/g were obtained. The influence of Mn loading and the nature of precursors on the solids properties were studied. The catalytic properties were studied in the model reactions of total oxidation of benzene and toluene. Molten salt derived solids demonstrated advantageous catalytic activity as compared to the reference catalysts. ZrO 2-supported catalyst prepared using KMnO 4 precursor showed the highest performance for the combustion of both aromatic hydrocarbons with T 50 values of 236 and 167 °C for benzene and toluene oxidation, respectively.

Oxidation of Benzyl Alcohol to Benzaldehyde by tert-Butyl Hydroperoxide over Nanogold Supported on TiO2 and other Transition and Rare-Earth Metal Oxides

Liquid-phase oxidation of benzyl alcohol to benzaldehyde by tertiary butyl hydroperoxide (at 95 °C) over nanogold supported on TiO2 and other transition-metal oxides (viz, MnO2, Fe2O3, CoOx, NiO, CuO, ZnO, and ZrO2) or rare-earth oxides (viz, La2O3, Sm2O3, Eu2O3, and Yb2O3) by the homogeneous deposition−precipitation (HDP) method has been investigated. The Au/TiO2 catalyst, prepared using the HDP method, showed high activity and selectivity in the reaction. The ZrO2-supported nanogold catalyst (HDP) also showed very good performance. The Au/TiO2 catalyst that was prepared using the deposition−precipitation (DP) method, however, showed poor catalytic activity, mostly because of its much-lower gold loading and/or lower Au3+/Au0 ratio. Irrespective of the catalyst preparation method, the catalytic activity increased as the gold loading increased. The gold deposition method strongly influenced the amount of gold that was deposited on TiO2, the gold particle size distribution, and also the surface Au3+/Au0 rat...

Slurry Impregnation of ZrO2 Extrudates: Controlled EggShell Distribution of MoO3, Hydrodesulfurization Activity, Promotion by Co

Catalysts with eggshell/uniform Mo concentration profiles were prepared by a reaction of ZrO2 and ZrO(OH)2 extrudates with an aqueous slurry of MoO3. The thickness of the shell was regulated by the amount of MoO3. CoCO3 was adsorbed onto MoO3/ZrO2 from its aqueous slurry. The ZrO2-supported catalysts were compared to their TiO2-supported and industrial reference Al2O3-supported counterparts in a model reaction of benzothiophene hydrodesulfurization.

Benzene oxidation with ozone over supported manganese oxide catalysts: Effect of catalyst support and reaction conditions

Catalytic oxidation of gaseous benzene with ozone was carried out over supported manganese oxides to investigate the factors controlling the catalytic activities. The rate for benzene oxidation linearly increased with the surface area of catalyst, regardless of the kinds of catalyst support, whereas the ratio of ozone decomposition rate to benzene oxidation rate was larger for SiO 2-supported catalyst than Al 2O 3-, TiO 2-, and ZrO 2-supported catalysts. The rate for benzene oxidation and CO x selectivity increased with the reaction temperature (22–100 °C) and were improved by the addition of water vapor to reaction gases. Benzene conversion and carbon balance increased with ozone concentration.

Zirconia-supported bimetallic RhPt catalysts: Characterization and testing in autothermal reforming of simulated gasoline

The behavior of ZrO2-supported RhPt catalysts was studied in the autothermal reforming of simulated gasoline to produce fuel gas (H2, CO, CO2, CH4, and H2O) suitable for solid oxide fuel cell applications.The bimetallic catalysts were superior to the monometallic Rh and Pt catalysts, and only a small addition of Rh increased the activity of the Pt catalyst markedly. Moreover, the reforming selectivity and the stability of bimetallic RhPt catalysts against carbon deposition improved with increasing Rh/Pt molar ratio.Strong synergism between Rh and Pt was observed, leading to excellent catalytic performance. Based on TPR-, SEM-, and EDX-results a Rh-Pt-O ternary system with RhxPt1−x–Rh2O3 equilibrium is suggested for the bimetallic catalysts, where Rh2O3 is the active site.

Catalytic abatement of acetaldehyde over oxide-supported precious metal catalysts

Catalytic combustion of acetaldehyde was investigated on various oxide-supported metal catalysts prepared by impregnation method. Among the as-calcined catalysts tested, SnO2-supported precious metal catalysts showed the highest activity at low temperatures despite low BET surface area, whereas the catalytic activity of the SnO2-supported samples was significantly degraded by reduction treatment in H2 atmosphere. The catalytic activity of ZrO2- and CeO2-supported metal catalysts was improved by reduction treatment, as compared with the as-calcined catalysts. Among the reduced catalysts, ZrO2-supported metal catalysts exhibited the highest activity for acetaldehyde combustion. To reveal these phenomena, all the catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and BET surface area. The catalytic activity was strongly related to the surface species easily reducible at low temperatures. Over the as-calcined SnO2-supported catalysts, Pt particles were highly dispersed and the existence of platinum species reducible at room temperature was inferred from XPS and TPR, which disappeared by the H2 reduction treatment, leading to deterioration of the activity. On the other hand, over the ZrO2- and CeO2-supported samples, precious metal species were reduced to metallic state by the H2 reduction treatment and stabilized to maintain the enhanced catalytic activity under oxidative atmosphere during acetaldehyde combustion.

Bifunctional catalysts for single-stage water–gas shift reaction in fuel cell applications.: Part 1. Effect of the support on the reaction sequence

Oxide support plays a significant role in the mechanistic reaction sequence for the water–gas shift (WGS) reaction over Pt-based catalysts. In situ FTIR spectroscopic and transient kinetic studies have been used to follow the reactions that occur. CeO 2-, TiO 2-, and ZrO 2-supported Pt catalysts have been studied at 300 °C. In all cases, CO is adsorbed on Pt. The role of the support oxide is to activate water, completing the WGS reaction sequence. We have taken into consideration four different pathways that may be involved in the complex WGS reaction scheme: (A) red–ox route, (B) associative formate route, (C) associative formate route with red–ox regeneration of the oxide support, and (D) carbonate route. In the case of Pt/ZrO 2, the WGS reaction follows the associative formate route with red–ox regeneration (route C). On Pt/TiO 2, both the red–ox route (A) and the associative formate route with red–ox regeneration (C) contribute. The associative formate route (B) is the relevant reaction pathway on Pt/CeO 2.

Catalytic combustion of methane over nano ZrO 2-supported copper-based catalysts

The nano ZrO 2-supported copper-based catalysts for methane combustion were investigated by means of N 2 adsorption, TEM, XRD, H 2-TPR techniques and the test of methane oxidation. Two kinds of ZrO 2 were used as support, one (ZrO 2-1) was obtained from the commercial ZrO 2 and the other (ZrO 2-2) was issued from the thermal decomposition of zirconium nitrate. It was found that the CuO/ZrO 2-2 catalyst was more active than CuO/ZrO 2-1. N 2 adsorption, H 2-TPR and XRD measurements showed that larger surface area, better reduction property, presence of tetragonal ZrO 2 and higher dispersion of active component for CuO/ZrO 2-2 than that of CuO/ZrO 2-1. These factors could be the dominating reasons for its higher activity for methane combustion.

An investigation of possible mechanisms for the water–gas shift reaction over a ZrO 2-supported Pt catalyst

The present work investigates the reactivity of the surface species observable by in situ DRIFTS formed over a Pt/ZrO 2 during the water–gas shift (WGS) reaction. A DRIFTS cell/mass spectrometer system was operated at the chemical steady state during isotopic transients to yield information about the true nature (i.e., main reaction intermediate or spectators) of adsorbates. Only carbonyl and formate species were observed by DRIFTS under reaction conditions; the surface coverage of carbonate species was negligible. Isotopic transient kinetic analyses revealed that formates exchanged uniformly according to a first-order law, suggesting that most formates observed by DRIFTS were of the same reactivity. In addition, the time scale of the exchange of the reaction product CO 2 was significantly shorter than that of the surface formates. Therefore, a formate route based on the formates as detected by DRIFTS can be ruled out as the main reaction pathway in the present case. The number of precursors of the reaction product CO 2 was smaller than the number of surface Pt atoms, suggesting that carbonyl species or some “infrared-invisible” complex (not excluding formates) at the Pt–zirconia interface was the main reaction intermediate. A simple redox mechanism could also explain the present results.

Low Temperature and H2 Selective Catalysts for Ethanol Steam Reforming

Supported Rh catalysts have been developed for selective H2 production at low temperatures. Ethanol dehydration is favorable over either acidic or basic supports such as γ-Al2O3 and MgAl2O4, while ethanol dehydrogenation is more favorable over neutral supports. CeO2–ZrO2-supported Rh catalysts were found to be especially effective for hydrogen production. We focused on a support prepared by a co-precipitation method having composition Ce0.8Zr0.2O2. A 2%Rh/Ce0.8Zr0.2O2 catalyst, prepared via impregnation without pre-calcination of support, exhibited the highest H2 yield at 450 °C among various supported Rh catalysts evaluated in this study. This may be due to both the strong interaction between Rh and Ce0.8Zr0.2O2 and the high oxygen transfer rate favoring reforming of acetaldehyde instead of methane production.

Structure characterization of Pt-Re/TiO 2 (rutile) and Pt-Re/ZrO 2 catalysts for water gas shift reaction at low-temperature

Pt-Re/TiO 2 (R: rutile) and Pt-Re/ZrO 2 catalysts, which have superior catalytic activity for the water gas shift reaction at low temperature (LT-WGS), were characterized by TEM and XPS measurements in order to examine the role of Re in enhancing catalytic activity. For the TiO 2 (R)-supported catalysts, TEM micrographs showed that Pt dispersion increased by Re addition to Pt/TiO 2 (R). XPS spectra indicated that the electronic interaction between Pt and Re on the TiO 2-supported catalysts is stronger than that on the ZrO 2-supported catalysts, and that the state of Re was stable on Pt-Re/TiO 2 (R) under the LT-WGS conditions. These results indicate that one of reasons for the superior catalytic activity of Pt-Re/TiO 2 (R) catalyst is an increase in Pt dispersion. The stable Re acts as anchors for Pt particles, resulting in high Pt dispersion. On the other hand, for the ZrO 2-supported catalysts, TEM micrographs showed that the Pt dispersion decreased by Re addition to Pt/ZrO 2. XPS spectra indicated that the interaction between Re and support on Pt-Re/ZrO 2 catalysts is stronger than that on Pt-Re/TiO 2 (R), and that the redox reaction between Re 4+ and Re 7+ was repeated on Pt-Re/ZrO 2 in the course of the LT-WGS reaction. These results suggested that the Re redox reaction significantly contributes to the high catalytic activity of the Pt-Re/ZrO 2 catalyst, although Pt-Re/ZrO 2 had lower Pt dispersion than Pt/ZrO 2. Therefore, it was determined that the additive effect of Re on Pt dispersion and catalytic activity was largely affected by the state of Re.

Catalytic vapor-phase oxidation of 2,2,2-trifluoroethanol

The synthesis of trifluoroacetaldehyde by vapor-phase oxidation of 2,2,2-trifluoroethanol using supported vanadium catalysts was studied. Significant differences were observed in the reaction outcomes resulting from different types of catalysts. The ZrO 2- and Al 2O 3-supported catalyst demonstrated both high catalytic activity and selectivity. The addition of co-catalysts such as MoO 3 or SnO 2 improved catalytic performance (Selectivity: up to 91%; S.T.Y.: >200 g L −1 h −1). The experimental results on catalyst lifetime showed a marked decrease in the activity of the Al 2O 3-supported catalyst within tens of hours, while the ZrO 2-supported catalyst showed little, if any, performance alterations for 2000 h.

Effect of Si addition on the properties of nanocrystalline ZrO2-supported cobalt catalysts

This study shows that Si addition during the glycothermal synthesis of nanocrystalline zirconia modified the properties of the zirconia, i.e. particle morphology and crystallite size, resulting in an improvement in the catalytic performance of Co/ZrO2catalysts in CO hydrogenation.

A model catalyst approach to the effects of the support on Co–Mo hydrodesulfurization catalysts

Co–Mo model sulfide catalysts, in which CoMoS phases are selectively formed, were prepared by means of a CVD technique using Co(CO) 3NO as a precursor of Co. It is shown by means of XPS, FTIR and NO adsorption that CoMoS phases form selectively when the Mo content exceeds monolayer loading. A single exposure of MoS 2/Al 2O 3 to a vapor of Co(CO) 3NO at room temperature fills the edge sites of the MoS 2 particles. It is suggested that the maximum potential HDS activity of MoS 2/Al 2O 3 and Co–Mo/Al 2O 3 catalysts can be predicted by means of Co(CO) 3NO as a “probe” molecule. An attempt was made to determine the fate of Co(CO) 3NO adsorbed on MoS 2/Al 2O 3. The effects of the support on Co–Mo sulfide catalysts in HDS and HYD were investigated by use of CVD-Co/MoS 2/support catalysts. XPS and NO adsorption showed that model catalysts can also be prepared for SiO 2-, TiO 2- and ZrO 2-supported catalysts by means of the CVD technique. The thiophene HDS activity of CVD-Co/MoS 2/Al 2O 3, CVD-Co/MoS 2/TiO 2 and CVD-Co/MoS 2/Al 2O 3 is proportional to the amount of Co species interacting with the edge sites of MoS 2 particles or CoMoS phases. It is concluded that the support does not influence the HDS reactivity of CoMoS phases supported on TiO 2, ZrO 2 and Al 2O 3. In contrast, CoMoS phases on SiO 2 show catalytic features characteristic of CoMoS Type II. With the hydrogenation of butadiene, on the other hand, the Co species on MoS 2/TiO 2, ZrO 2 and SiO 2 have the same activity, while the Co species on MoS 2/Al 2O 3 have a higher activity.

Vapor-phase Beckmann rearrangement of cyclohexanone oxime over B 2O 3/TiO 2-ZrO 2

Pure TiO 2, ZrO 2 and TiO 2-ZrO 2 mixed oxides with various compositions were prepared by the co-precipitation method. Catalysts containing 12 wt.% boria were prepared using these oxides and their catalytic performance for vapor-phase Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam was determined. With increasing zirconia content in the mixed oxide, the specific surface area and the temperature of the phase transformation increased; maximum values were obtained for a mixed oxide having a Ti and Zr molar ratio of 1/1. XRD results indicated that TiO 2-ZrO 2 became amorphous after calcination at 500 °C if neither the content of TiO 2 nor that of ZrO 2 was less than 25%. The yield of lactam increased with increasing zirconia content in mixed oxide and reached a maximum value for the B 2O 3/TiO 2-ZrO 2 (1/1) catalyst. With further increase in zirconia content, the lactam yield decreased; the lowest value was observed for the pure ZrO 2-supported catalyst. The acidic property and the pore characteristics of the catalyst were key factors that affected its performance. The influences of the operating parameters on the performance of B 2O 3/TiO 2-ZrO 2 (1/1) catalyst were also investigated.

Alumina- and Alumina–Zirconia-Supported PtSn Bimetallics: Microstructure and Performance for the n-Butane ODH Reaction

In the present work, a number of Al2O3- and Al2O3–ZrO2-supported catalysts were prepared and studied. The microstructure of the particles formed in these systems was analyzed by high-resolution electron microscopy (HREM). HREM images of Al2O3-supported catalysts revealed a broad particle-size distribution, with a major Pt phase exhibiting diameters in the range 5–15 nm with a shell of PtSn4. Also, PtSn4 and very large particles were detected. In the case of Al2O3–ZrO2-supported catalysts, ZrO2 was present as nanometer-size crystals of the tetrahedral and monoclinic phases and the trimodal distribution of metal particles disappeared, the smaller particles being dominant. Photoelectron spectroscopy showed that in used catalysts tin is oxidized while platinum remains partially reduced. Upon activation (reduction at 623 or oxidation at 773 K/reduction at 873 K), tin became partially reduced; however, no significant changes were seen in the oxidation state of platinum. The catalysts were tested in the oxidative dehydrogenation of n-butane. The major reaction products were carbon oxides and olefins, with much smaller amounts of cracking and isomerization products. The incorporation of tin into the Pt/Al2O3 catalyst led not only to an increase in conversion but also to an inhibition of cracking reactions. Deactivation was observed in all cases. Surface analysis by photoelectron spectroscopy of exhausted catalysts revealed the formation of carbonaceous deposits on the catalyst surface, indicating that coking is responsible for catalyst deactivation.