Zirconia Support Research Articles

Boosting CO2 hydrogenation via size-dependent metal–support interactions in cobalt/ceria-based catalysts

Metal–support interactions have a strong impact on the performance of heterogeneous catalysts. Specific sites at the metal–support interface can give rise to unusual high reactivity, and there is a growing interest in optimizing not only the properties of metal particles but also the metal–support interface. Here, we demonstrate how varying the particle size of the support (ceria–zirconia) can be used to tune the metal–support interactions, resulting in a substantially enhanced CO2 hydrogenation rate. A combination of X-ray diffraction, X-ray absorption spectroscopy, near-ambient pressure X-ray photoelectron spectroscopy, transmission electron microscopy and infrared spectroscopy provides insight into the active sites at the interface between cobalt and ceria–zirconia involved in CO2 hydrogenation to CH4. Reverse oxygen spillover from the support during treatment in hydrogen results in the generation of oxygen vacancies. Stabilization of cobalt particles by ceria–zirconia particles of intermediate size leads to oxygen spillover to the support during the CO2 and CO dissociation steps, followed by further hydrogenation of the resulting intermediates on cobalt. Metal–support interactions can effectively modify the catalytic properties of heterogeneous composites. Here, the authors report the possibility of controlling the interaction between cobalt and a ceria–zirconia support by changing the particle size of the latter, resulting in a superior CO2 hydrogenation system.

Physico-Chemical Properties of Nickel Promoted Sulfated Zirconia Powder Prepared using Different Procedures

In this work, nickel promoted sulfated zirconia (Ni/SZ) as catalyst was prepared by either by reflux (Ni/SZ-R) or hydrothermal Ni impregnation (Ni/SZ-H) routes. The aim of this study was to evaluate the influences of two preparative methods on the physico-chemical properties of prepared catalysts. Both the catalysts were characterized by XRD, FTIR, ammonia adsorption, SEM-EDX, TEM-SAED, AAS and BET. It was found that the presence of sulfate and nickel could enhance the Brønsted and Lewis active acid sites. In relation to the effect of Ni impregnation method, acidity, amount of sulfate and Ni found in Ni/SZ-R were higher than those in Ni/SZ-H. Unfortunately, higher impregnated sulfate and nickel on zirconia support led to a decrease in surface area and pore volume and an increase in crystallite size of grainy aggregated mesoporous nickel promoted sulfated zirconia (Ni/SZ).

Unraveling the effect of ZrO2 modifiers on the nature of active sites on AuRu/ZrO2 catalysts for furfural hydrogenation

Ru and AuRu nanoparticles were prepared by a sol-immobilization methodology and deposited on different doped zirconia supports (ZrO2, Y–ZrO2 and La–ZrO2).

Zirconia supported nickel catalysts for glycerol steam reforming: Effect of zirconia structure on the catalytic performance

The effect of the zirconia structure in Ni/ZrO2 catalysts on the glycerol steam reforming (GSR) reaction was studied. A tetragonal zirconia support was synthesized via a hydrolysis technique and loaded with 5 wt% Ni via a wet-impregnation method. Similarly, a commercial monoclinic zirconia support was also impregnated with 5 wt% Ni. Following calcination at 600 °C, physico-chemical properties of the prepared catalysts were investigated by X-Ray Diffraction (XRD), H2-Temperature Programmed Reduction (H2-TPR) and CO2-Temperature Programmed Desorption (CO2-TPD) techniques. The catalysts were then tested in the GSR reaction in the 400–700 °C range with a steam to glycerol molar ratio of 9:1 and a flow rate of 0.025 mL/min. The monoclinic catalyst exhibited a better performance giving higher hydrogen yields and glycerol conversions. This was attributed to an improved reducibility of Ni in this catalyst. Stability tests at 600 °C revealed the deactivation of the tetragonal catalyst during 6 h as a result of the formation of encapsulating coke which blocked active Ni metal sites. The monoclinic catalyst, exhibiting the formation of only filamentous coke, remained relatively stable for 24 h.

Comparison of carbon deposition features between Ni/ZrO2 and Ni/SBA-15 for the dry reforming of methane

Ni-based catalysts supported on ZrO2 and SBA-15 were employed in dry reforming of methane. The relation between carbon deposition and the deactivation of supported Ni catalysts was studied. Ni/ZrO2 exhibited superior stability, despite of its high coking rate. Therefore, there was no direct relationship between the coking rate and the deactivation rate. In order to investigate the nature of the coke species during dry reforming of methane, TG-DTA/CO2-TPO/TPSR/TEM experiments were conducted on the spent catalysts. Characterization results showed that the formation of CNTS on Ni/ZrO2 could be responsible for the superior stability. For comparison, the dominant carbon species was encapsulating carbon on Ni/SBA-15, leading to serious deactivation. The main difference between Ni/ZrO2 and Ni/SBA-15 was the reactivity of carbon species towards carbon dioxide. Coke deposited on Ni/ZrO2 was oxidized by CO2 at lower temperature, although carbon species on the two catalysts was similar. Additionally, the results of TPSR illustrated that the surface oxygen species over the zirconia support was involved in the oxidation of coke by CO2. The activity of Ni/ZrO2 was completely restored after the in-situ regeneration with CO2, indicating that carbon deposition was greatly removed by CO2.

A computational-experimental investigation on high ethylene selectivity in ethanol dehydration reaction found on WOx/ZrO2-activated carbon bi-support systems

The high ethylene selectivity exhibited on the zirconia-activated-carbon bi-support catalyst is investigated by experiment and density functional theory–based (DFT) analysis. This bi-support catalyst systems prepared by the physical mixing method for the tungsten catalyst show a significant increase in ethylene selectivity up to 90% compared to the zirconia single support system (~58%) during the ethanol dehydration reaction. Besides, the optimal percent weight ratio of zirconia to activated carbon, which results in the highest ethanol conversion is 50:50. The DFT–based analysis is used to investigate high ethylene selectivity in the bi-support system. It shows that the WO5/zirconia is the most stable model for the zirconia single-support tungsten catalyst represented by the zirconia (101) facet of the tetrahedral phase. The carbon atoms were added to the WO5/zirconia to model the tungsten catalyst on the bi-support system. The Bader charge analysis is carried out to determine the electron transfer in the catalyst. The bonding between ethylene and the WO5 active site on the catalyst is weakened when the system is bi-support, where the added carbon atoms on the catalyst in the ZrO2 region decrease the ethylene adsorption energy. Thus, the desorption and the selectivity of ethylene are promoted. The decrease in adsorption energy can be explained via the analysis of the projected density of states (PDOS) profiles of atom involving the adsorption. It was found that the added carbon in the ZrO2 region induces the electron transfer from the ethylene molecule to the surface, especially to the ZrO2 region. The depletion of the electron around the ethylene molecule weakens the bonds, thus, promote desorption. Hence, the advantages of using the bi-support system in the tungsten catalyst are that the catalyst exhibit (1) high conversion due to the zirconia support and (2) high ethylene selectivity due to the added carbon promoting the desorption of ethylene via the induction of electron from an ethylene molecule to surface.

A MOF-templated approach for designing ruthenium–cesium catalysts for hydrogen generation from ammonia

Ammonia is regarded as a safe hydrogen energy carrier due to its high hydrogen content and narrow flammable range. Herein, we report a novel metal-organic framework (MOF) templated approach to synthesize highly active catalysts for the hydrogen production from ammonia. Calcination of ruthenium-impregnated UiO-66(Zr)-NH2 leads to formation of small ruthenium nanoparticles (<3 nm) with a strong interaction with the resulting mesoporous zirconia support. These catalysts present a turnover frequency considerably higher than Ru/CNTs catalysts, defying the established believe of 3–5 nm as optimum Ru size for this reaction. Moreover, cesium promoter acts as an electronic modifier of Ru and also as a molecular spacer enhancing the stability under reaction conditions. Despite the exciting potential of this approach, the collapse of MOF framework structures during the calcination process limits the accessibility with an estimated ~16% of the ruthenium accessible, underestimating the actual turnover frequency (TOF) values.

Ni-YSZ a New Support for Proton Conducting Fuel Cells

In this research, the possibility of reducing the YSZ content inside the Ni-YSZ support of tubular solid oxide fuel cells (SOFCs) based on proton conducting electrolyte material BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) is studied. The cell consists of a Ni-yttria stabilized zirconia (YSZ) support (with different Ni:YSZ ratios), Ni-BZCYYb anode functional layer (AFL), BZCYYb electrolyte and LSCF-BZCYYb cathode. The results indicate that the addition of only 10 wt% YSZ to the support improves the microstructure by preventing severe Ni grain growth, thereby providing higher density of active sites at the support/AFL interface and more uniform distribution of fuel gas to the active sites. The polarization resistance of the optimized cell with 10 wt% YSZ in the support is lower than the fully Ni supported cell. The promising results of this study reveal that Ni-YSZ can be a suitable support for proton conducting fuel cells.

Development of proton conducting fuel cells using nickel metal support

This research reports the fabrication of a metal supported fuel cell based on the well-known proton conducting electrolyte (PCE) BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) material. The impact of the addition of YSZ on the anode microstructure is also described. This solid oxide fuel cell (SOFC) consists of Ni:yttria stabilized zirconia (YSZ) support (with different weight ratios of Ni:YSZ), Ni-BZCYYb anode functional layer (AFL), BZCYYb electrolyte and LSCF-BZCYYb cathode. The results show that addition of only 10 wt% YSZ to the support improves the microstructure of the cell by preventing severe Ni grain growth inside the support, and providing more accessible triple phase boundaries (TPBs) at the contact surface of the support/AFL and better distribution of the fuel gas to the accessible TPBs. As a result of microstructural improvement, polarization resistance of the cells with 10 wt% YSZ decreases compared with the cell having pure Ni metal. The cell containing YSZ in the support shows 67 h of stable operation under potentiostatic SOFC condition without any degradation. The current metal supported tubular fuel cell shows promising electrochemical and microstructural features which has the possibility to replace the conventional (Ni-PCE) or even Ni-YSZ anode supports.

Synthesis of supported ZSM-5 nanoparticles

Abstract The influence of the support on the nucleation of ZSM-5 nanoparticles has been studied for three supports: γ-alumina, zirconia and carbon nanotubes (CNT). While zeolite nucleation was suppressed in presence of alumina and strongly delayed in presence of zirconia, it occurred without delay in presence of CNT. These differences are explained by the partial dissolution of the support (for alumina and zirconia supports) that modify the composition of the zeolite nucleation solution. For the CNT/zeolite sample, the obtained composite contains about 60 wt% of zeolite and develops a surface area of 776 m2 g−1.

Size, nanostructure, and composition dependence of bimetallic Au–Pd supported on ceria–zirconia mixed oxide catalysts for selective oxidation of benzyl alcohol

A bimetallic Au–Pd catalyst supported on ceria–zirconia with Au:Pd molar ratio 0.8 has been synthesized using a simultaneous deposition–precipitation method and oxidized at 250, 450, and 700 °C in order to modify its particle size, nanostructure, and composition. Combined X-ray energy dispersive spectroscopy (XEDS) and X-ray photoelectron spectroscopy (XPS) analysis clearly evidence that the bimetallic Au–Pd catalyst oxidized at 250 °C is made up of a mixture of monometallic Au and Pd and bimetallic Au–Pd nanoparticles with Au:Pd ratios varying over a wide range. Increasing oxidation temperature leads to a stronger interaction between Au and Pd. Meanwhile, a slight increase of particle size and a narrowing of the Au:Pd ratio in the bimetallic nanoparticles take place. Compared with titania and activated carbon supports, the resistance against sintering at high temperatures of Au–Pd metal particles supported on ceria–zirconia is proven to be higher. A synergistic effect has been observed for selective oxidation of benzyl alcohol on these catalysts. The catalytic activity decreases only slightly after oxidation at 450 °C. However, oxidation at 700 °C results in much lower catalytic activity. Migration of Pd onto Au particles during oxidation of benzyl alcohol enhances the catalytic activity of a physical mixture of monometallic Au and Pd supported on ceria–zirconia catalysts. This fact, jointly with an analysis of the intrinsic activity, reveals the influence of the actual nature of Au–Pd interactions in the bimetallic particles, which points to higher activity of Au@Pd or AuPd@Pd nanostructures on ceria–zirconia supports.

Synthesis and Characterization of Zirconia Supported Silicotungstic Acid for Ethyl Levulinate Production

A Keggin silicotungstic acid (HPS) catalyst was heterogenized by loading (10–40 wt %) over zirconia support, and the resulting catalysts were named ESZN-1 (10 wt %), ESZN-2 (20 wt %), ESZN-3 (30 wt %), and ESZN-4 (40 wt %). After that, synthesized catalysts were characterized using several tools and techniques which revealed that the Keggin structure of the parent HPS catalyst remained intact after heterogenization. Eventually, synthesized catalyst performance evaluation tests were performed for the production of ethyl levulinate from biomass-derived levulinic acid under microwave heating irradiations. Under optimum operating conditions, more than 90% LA conversion with 100% EL selectivity was obtained at a 110 °C temperature in 30 min in the presence of 100 mg of ESZN-4 in a solution containing levulinic acid and ethanol in a 1:43 ratio. A kinetic study on LA conversion in the presence of the ESZN-4 catalyst revealed a pseudo-first-order mechanism for ethyl levulinate synthesis.

Organic acid-assisted preparation of highly dispersed Co/ZrO2 catalysts with superior activity for CO2 methanation

Various organic acids were investigated for preparing the highly dispersed cobalt catalysts on zirconia support, Co/ZrO2, by an acid-assisted incipient wetness impregnation. The organic acid-assisted preparation results in highly dispersed Co/ZrO2 catalysts which demonstrate superior catalytic activity with only 2 wt.% Co loading for CO2 methanation. Among the acids, the carboxylic acids with bigger molecular weight, more carboxyl groups and hydroxyl groups are more effective. Furthermore, the amino acids can also change the charge property of ZrO2 surface through controlling the solution pH and increase the metal dispersion through strong electrostatic adsorption. It is worth mentioning that, among the numerous organic acids, citric acid-assisted preparation gives Co/ZrO2 catalyst with superior catalytic activity and increased the CO2 conversion from 38% to 85% with highest turnover frequency. The linear relationship between metal dispersion and TOF with the molar ratio of acid to cobalt nCA/Co ranging from 0 to 2 demonstrates the importance of well dispersed metal particles in the enhanced activity. However, when the nCA/Co value exceeds 2 and the metal particle size further decreases, but no further enhancement is observed and the CO2 conversion even slightly decreased at the nCA/Co value of 5. The organic acids-assisted strategy can lead to increased metal dispersion and higher TOF for Co/ZrO2 catalysts; the appropriate metal dispersion corresponds to the suitable Co-ZrO2 interaction with oxygen vacancy which leads to more catalytically active sites for CO2 adsorption and catalytic hydrogenation. The organic acid-assisted strategy provides a new design approach for highly dispersed and active catalysts.

Mediating interaction strength between nickel and zirconia using a mixed oxide nanosheets interlayer for methane dry reforming

For many reactions balancing the degree of interaction between the metal catalyst and the underlying support material is pivotal for obtaining optimal catalytic performance. One important example is the reforming of methane contained in biogas, using CO2 as an oxidizer, to make syngas (H2 and CO). For this reaction to become industrially viable, the catalyst needs to be based on non-precious transition metals. Unfortunately, catalyst deactivation induced by metal sintering and coking remains a major challenge for this class of catalysts. Herein, we demonstrate the use of a ″surface phase oxide″ in the form of MgAl mixed oxide nanosheets (<2 nm thick), derived from layered double hydroxide, as an interlayer to mediate the interaction between nickel nanoparticles and an underlying zirconia support. This unique hierarchical catalyst configuration is shown to enhance conversion, under undiluted conditions and GHSV=240,000 cm3h−1gcat−1, by up to 2-fold, as compared to Ni supported on ZrO2 and by up to 15-fold as compared to Ni on bulk MgAl mixed oxide, keeping the catalyst stable over 240 h reaction times. To gain better understanding into the mechanism of enhanced catalytic performance we used a combination of PXRD, SAXS, Cryo-TEM, H2-TPR, STEM-EDS, and XPS in conjunction with the results for the catalytic performance. The combined results show that the amplified catalytic performance is strongly correlated with the modification of the metal-support interaction (MSI) by the MgAl mixed oxide interlayer. Although the physical interaction of Ni particles at the edges of the nanosheets with the underlying ZrO2 cannot be completely dismissed, all the available data shows no such interaction exists. Hence, the change in MSI in the stacked configuration is attributed to the indirect MSI effect of the underlying ZrO2 on the properties of the nickel catalyst. Overall the approach described here, for manipulating MSI to promote the challenging methane dry reforming, can be extended by replacing the underlying metal oxide support (commercial or custom made), synthesis of mixed oxide nanosheets of different A2+B3+ ratios and type, and changing the active metal catalyst.

Influence of Mg‐promoted Ni‐based Catalyst Supported on Coconut Shell Carbon for CO2 Methanation

AbstractThis study aims to investigate the conversion of CO2 and H2 into CH4 under atmospheric pressure. A series of nickel‐based catalysts using coconut shell carbon were prepared by co‐impregnation method, and the coconut shell carbon carrier in the CO2 methanation demonstrated its advantage by comparison with the alumina and zirconia supports. Magnesium modified Ni/coconut shell carbon catalysts were studied to explore the catalytic performances, the morphology and properties of all catalysts were characterized by CO2‐TPD, XRD, SEM, BET, FTIR, TEM and H2‐TPR. Catalytic performances were experimentally evaluated in a fixed bed tubular reactor under atmospheric pressure, WHSV of 10,000 mlh−1g−1, and H2/CO2 molar ratio of 4/1. Experimental results indicated magnesium modified Ni‐Mg0.26/coconut shell carbon catalyst has outstanding activity and excellent stability, which performed the highest CO2 conversion (90.10%) and CH4 selectivity (99.22%) at 450 °C. The catalytic activity of Ni‐Mg0.26/ coconut shell carbon experienced 50 h stability evaluation, and no evident decrease was found during the methanation process.

Performance of Pd-Based Membranes and Effects of Various Gas Mixtures on H2 Permeation

H2 permeation and separation properties of two Pd-based composite membranes were evaluated and compared at 400 °C and at a pressure range of 150 kPa to 600 kPa. One membrane was characterized by an approximately 8 μm-thick palladium (Pd)-gold (Au) layer deposited on an asymmetric microporous Al2O3 substrate; the other membrane consisted of an approximately 11 μm-thick pure palladium layer deposited on a yttria-stabilized zirconia (YSZ) support. At 400 °C and with a trans-membrane pressure of 50 kPa, the membranes showed a H2 permeance of 8.42 × 10−4 mol/m2·s·Pa0.5 and 2.54 × 10−5 mol/m2·s·Pa0.7 for Pd-Au and Pd membranes, respectively. Pd-Au membrane showed infinite ideal selectivity to H2 with respect to He and Ar at 400 °C and a trans-membrane pressure of 50 kPa, while the ideal selectivities for the Pd membrane under the same operating conditions were much lower. Furthermore, the permeation tests for ternary and quaternary mixtures of H2, CO, CO2, CH4, and H2O were conducted on the Pd/YSZ membrane. The H2 permeating flux decreased at the conclusion of the permeation tests for all mixtures. This decline however, was not permanent, i.e., H2 permeation was restored to its initial value after treating the membrane with H2 for a maximum of 7 h. The effects of gas hourly space velocity (GHSV) and the steam-to-carbon (S/C) ratio on H2 permeation were also investigated using simulated steam methane reforming mixtures. It was found that H2 permeation is highest at the greatest GHSV, due to a decline in the concentration polarization effect. Variations in S/C ratio however, showed no significant effect on the H2 permeation. The permeation characteristics for the Pd/YSZ membrane were also investigated at temperatures ranging from 350 to 400 °C. The pre-exponential factor and apparent activation energy were found to be 5.66 × 10−4 mol/m2·s·Pa0.7 and 12.8 kJ/mol, respectively. Scanning Electron Microscope (SEM) and X-ray diffraction (XRD) analyses were performed on both pristine and used membranes, and no strong evidence of the formation of Pd-O or any other undesirable phases was observed.

Impact of the modification method of Ni/ZrO2 catalyst by alkali and alkaline earth metals on its activity in thermo-chemical conversion of cellulose

The goal of this work is to determine an impact of the modification method of Ni/ZrO2 catalyst by alkali and alkaline earth metals on its activity in thermo-chemical conversion of cellulose to hydrogen-rich gas. MexO-ZrO2 supports (where Me = Ca, Mg, Na or K) were prepared by impregnation, precipitation and sol-gel methods. The obtained results reveal that an introduction of dopants to the zirconia support considerably enhances the H2 yield in comparison to unmodified catalyst. An increase in the hydrogen formation is accompanied by a rise in the total volume of the produced gases. It is demonstrated that the highest amount of hydrogen is formed in the presence of the catalysts containing CaO-ZrO2 support followed by Na doped materials. This phenomenon can be attributed to more efficient incorporation of Ca2+ and Na+ cations in the zirconia lattice making it more stable in the reaction conditions. Moreover, it is observed that an activity order of the investigated catalysts is consistent with the changes in the basic character of their surface.

Unraveling the Role of the Rh–ZrO2 Interface in the Water–Gas-Shift Reaction via a First-Principles Microkinetic Study

The industrially important water–gas-shift (WGS) reaction is a complex network of competing elementary reactions in which the catalyst is a multicomponent system consisting of distinct domains. Herein, we have combined density functional theory calculations with microkinetic modeling to explore the active phase, kinetics, and reaction mechanism of the WGS over the Rh–ZrO2 interface. We have explicitly considered the support and metal and their interface and find that the Rh–ZrO2 interface is far more active toward WGS than Rh(111) facets, which are susceptible to CO poisoning. CO2 forming on the zirconia support rapidly transforms into formate. These findings demonstrate the central role of the interface in the water–gas-shift reaction and the importance of modeling both the support and the metal in bifunctional systems.

Synthesis and characterization of Keggin-type polyoxometalate/zirconia nanocomposites—Comparison of its photocatalytic activity towards various organic pollutants

Heteropolyacid supported ZrO2 nanocomposites has been prepared through wet impregnation method with the intention to improve the photodegradation performance under UV light. The material consist of mixed monoclinic and cubic ZrO2 phase and orthorhombic Keggin type 12- phosphotungstic acid(PTA) with different ratios. The phase structure, chemical composition and oxidation state of the elements tungsten (W), zirconia (Zr) were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). In addition, Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, Diffuse Reflectance Ultraviolet–Visible Spectroscopy (DRS-UV–Vis) were carried out to confirm the presence of functional group and optical absorption properties. Surface area of the synthesized composite was analyzed by BET analysis and morphology was confirmed using high resolution scanning electron microscopy (HR-SEM) and high resolution transmission electron microscopy (HR-TEM) and the results reveal that PTA is chemically bonded to zirconia support which confirms that the sample was synthesized successfully. The heterogeneous photocatalytic activity of the composites were studied by using aqueous solution of various organic pollutants such as methylene blue (MB), methyl orange (MO), rhodamine B (Rh-B), crystal violet (CV), bromo cresol green (BCG) dyes, 4- Nitrophenol and 2,4- Dichlorophenoxy acetic acid under UV light illumination. It is found that each dye needs different specific ratio of nanocomposite to degrade efficiently at a given time interval.

Insight into the effect of metal and support for mild hydrodeoxygenation of lignin-derived phenolics to BTX aromatics

Hydrodeoxygenation (HDO) of lignin-derived phenolics, including the reactions of hydrogenation and dehydration, is an efficient method for production of bio-based aromatic hydrocarbons. The purpose of this study was to explore the catalytic performance of different metals as hydrogenation active sites (Pd, Ru, Cu and Ni) and mild acidic supports (ZrO2, CeO2 and ZrCeO2) as dehydration promoter in order to enhance the HDO efficiency under mild reaction conditions (temperature <350 °C, pressure: 1 atm). Rhenium oxide was added to all catalysts to increase catalyst acidity for an enhanced dehydration activity. m-Cresol and guaiacol were used as phenolic lignin model compounds. Zirconia showed better performance than ceria as a result of its higher acid density. The hydrogenation activity order of metals was as follows: Pd > Ni > Ru > Cu. All the hydrogenation metals selectively promoted the hydrogenation of carbonyl group, and led to the selective formation of aromatic hydrocarbons. The catalyst of PdReOx/ZrO2 was used for HDO of m-cresol in the temperature range of 250–300 °C, and almost retained its entire catalytic activity by temperature reduction. This is due to the mild acid strength induced by zirconia support and rhenium oxide which do not cause phenolic adsorption and trapping at atmospheric pressure and low temperatures.