Zirconia Support Research Articles

N-Alkane hydroconversion over carbided molybdena supported on sulfated zirconia

A carbided molybdena on sulfated zirconia support has been prepared by in situ exposure to a methane/hydrogen mixture at 650 °C and the characteristics established using N2 adsorption and X-ray diffraction. The activity of the catalyst in the hydroconversion of C6 to C9n-alkanes was investigated in the temperature range 350–450 °C at 1 atm pressure. Activity and selectivity were found to show strong dependence on the choice of n-alkane with reaction rates found to be higher for the shorter alkanes. n-Hexane and n-heptane were hydroisomerised to the corresponding C6 and C7 isomers with high selectivity while the higher alkanes, especially nonane, produced mainly hydrocracking products. The catalyst offers a potential system for the upgrading of light naphtha range paraffins.

Coextrusion of Zirconia–Iron Oxide Honeycomb Substrates for Solar-Based Thermochemical Generation of Carbon Monoxide for Renewable Fuels

Ceramic honeycombs based on homogeneous composites of zirconia and iron oxide are formed using polymer-based coextrusion for testing in thermochemical reactors to generate CO for renewable fuels. The honeycomb substrates possess controlled surface areas and are processed using zirconia with 3 and 8 mol % yttria additions to investigate the influence of surface area and oxygen conductivity of the substrate on the CO generation properties. CO generation was tested using a gas chromatography mass spectrometer and a laboratory scale thermochemical reactor capable of precisely controlling temperature and gas conditions. Results showed that reaction temperature and reactant gas flow rate effect CO generation. The yttria content of the zirconia support phase was also found to have a significant impact on the long-term CO generation, improving iron oxide conversion from 41 to 58%. Yttria content did not markedly impact the short-term reaction properties. Increasing the surface area of the substrates, from 2.6 up ...

Steam reforming of ethanol over carburized alkali-doped nickel on zirconia and various supports for hydrogen production

The steam reforming of ethanol over carburized alkali-, La- and Ce-doped nickels on zirconia and various supports was studied to determine the support effects, alkali addition and carburization. The 823 K-carburized Ni/ZrO 2 and Ni/V 2O 5 catalysts exhibited higher activities than the Ni catalysts supported on CeO 2, Al 2O 3, SiO 2–Al 2O 3 and MgO and a reduced catalyst. The cesium-doped Ni/ZrO 2 promoted more hydrogen formation than the Li-, K-, La- and Ce-doped catalysts. From the XRD measurement, crystals of ZrO 2, Ni carbide and Ni metal were formed during the carburization of the Ni/ZrO 2 catalyst at 823 K. No Ni carbide was observed on the MgO, CeO 2 Al 2O 3, and V 2O 5 carburized catalysts. The Cs 0.2Ni/ZrO 2 and Cs 0.5Ni 0.5/Zr exhibited no carbon deposition at 7 h. The carburized and cesium-doped Ni/ZrO 2 was more effective in decreasing the carbon deposition. From the IR study, the formed carbonated species were attributed to the formation of CO 3 − from the formed CO 2 (CO 2 + O 2 − → CO 3 −). In the pulse experiment of H 2 18O, Cs 0.2Ni/ZrO 2 helped to facilitate the dissociation of H 2O to 2H and O and the decomposition of CH 3CHO to hydrogen and CO 2 through the CH 3CO species. The TPD after ethanol adsorption on Ni/ZrO 2 with and without Cs-doping showed that the Cs-doped Ni/ZrO 2 catalyst promoted the C–H breaking through the CH 3CO species more than the Ni/ZrO 2 catalyst.

MOx (M = Mn, Fe, Ni or Cr) improved supported Co3O4 catalysts on ceria–zirconia nanoparticulate for CO preferential oxidation in H2-rich gases

This approach dealt with the modification of our developed Co3O4/Ce0.85Zr0.15O2 catalysts with transition metal oxides MOx (M=Mn, Fe, Ni or Cr) for CO preferential oxidation (CO PROX) in H2-rich gases. Results showed that just MnOx modification remarkably broadened the temperature window of 100% CO conversion, also better than those in the report about Co-Mn composite catalysts from another research group. And even in the presence of H2O and CO2, the 175–225°C temperature range for almost 100% CO conversion can be achieved over the optimized catalyst. Moreover, the addition of MnOx significantly improved the catalytic activity and selectivity, which was dramatically better than those of the supported MnOx or Co3O4 catalysts on ceria–zirconia nanoparticulate, indicating the existence of the remarkable Co-Mn synergistic effect. The MnOx modified supported Co3O4 catalysts exhibited outstanding catalytic properties for CO PROX reaction, which was strongly dependent on the reducibility and dispersion of the active species affected by the Co/Mn atomic ratio and loading. The XRD and H2-TPR techniques were performed to reveal the effect of structure–activity relationship on the catalytic properties. The analytic results presented that Co3+ was the main active species for CO PROX reaction, and the existence of Mn4+ and Mn3+ was also favorable to the reaction. The XRD and H2-TPR characterization results affirmed the existence of strong interaction between Co and Mn, increasing the ratio of Co3+/Co2+ resulted from the electron transfer between Co2+ and Mn4+. Besides the improvement of Co3O4 dispersion and the enlargement of the Co3+/Co2+ ratio through Co-Mn interaction, the addition of MnOx could improve the stability of the ceria–zirconia support through the metal–support interaction. As a result, the CO selective oxidation reaction was efficiently improved. The 16wt.%Co3O4-MnOx/Ce0.85Zr0.15O2 (Co/Mn=8:1) could be a quite potential catalyst for eliminating trace CO from H2-rich gases.

Production of hydrogen via steam reforming of bio-oil over Ni-based catalysts: Effect of support

Nickel-based catalysts supported on zirconia (Ni/ZrO 2) were prepared, characterized and tested for the production of hydrogen via steam reforming of bio-oil. The effects of metal loading on the hydrogen (H 2) and carbon monoxide (CO) yields and the carbon deposition percentage were investigated. In order to examine the effect of support, the results obtained on zirconia support were compared to the results obtained over nickel-based catalysts supported on alumina (Ni/Al 2O 3). It was found that the Ni/ZrO 2 catalysts presented higher activity than those supported on alumina for hydrogen production. The CO yields obtained over Ni/ZrO 2 catalysts were also higher than those obtained over Ni/Al 2O 3 catalysts. A potential H 2 yield of almost 80% can be obtained at 850 °C using Ni/ZrO 2 catalysts with a nickel content of 14%; whereas, the H 2 yield was less when Ni/Al 2O 3 catalysts were employed. The amount of carbon deposited on each catalyst was measured. It was observed that the carbon depositions on the Ni/ZrO 2 catalysts were extremely high. A comparison between the amounts of carbon deposited on the Ni/Al 2O 3 and Ni/ZrO 2 catalysts revealed that the carbon deposition is strongly dependent on the type of support.

Acid and redox properties of tungstated zirconia catalysts

Various tungstated zirconia catalysts with a WO3 loading of about 16 wt% were characterized both in their acid and oxidation properties. The samples have been characterized in their micro-structural and surface properties by BET, X-ray diffraction, Raman spectroscopy, temperature programmed reduction, elemental chemical analysis. The surface acidity was determined by the techniques of NH3 adsorption microcalorimetry and pyridine infrared spectroscopy (FT-IR). Improved acidity has been detected upon addition of WO3 to zirconia by both techniques. The global acid strength and the total number of acid sites increased greatly with the formation of WOx clusters on the zirconia support. This acidity increase can be attributed to the creation of Bronsted acid sites generated by the well dispersed WOx domains, as observed by FT-IR pyridine desorption.

Effect of oxide support surface area on hydrogenation activity: Pt/Ni bimetallic catalysts supported on low and high surface area Al 2O 3 and ZrO 2

Catalyst characterization and batch reactor studies have been performed to better understand the effects of oxide support and support surface area on low-temperature 1,3-butadiene hydrogenation over supported PtNi bimetallic catalysts. The supports studied in this work are: α-Al 2O 3 (10–16 m 2/g), γ-Al 2O 3 (80–120 m 2/g), low surface area ZrO 2 (20–30 m 2/g), and high surface area ZrO 2 (100–200 m 2/g). Transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS) were used to characterize the particle size and the extent of Pt–Ni bimetallic bond formation, respectively. The bimetallic catalysts supported on the two low surface area supports show larger metal nanoparticles; however, these catalysts also display greater extent of bimetallic bond formation, as characterized by the Pt L III-edge EXAFS. After normalizing the hydrogenation rate constants for the two alumina-supported catalysts by the CO uptake values, the two rate constants appear very similar, suggesting that the bimetallic nanoparticles have similar structures on the alumina supports. In contrast, normalizing the hydrogenation rate constants for the two zirconia catalysts reveals that the catalyst supported on the high surface area zirconia is approximately twenty times less active, suggesting a strong metal-support interaction (SMSI) between the metal nanoparticles and the high surface area zirconia support.

Hydrotreatment of wood-based pyrolysis oil using zirconia-supported mono- and bimetallic (Pt, Pd, Rh) catalysts

Fast pyrolysis oil (PO), the liquid product of fast pyrolysis of lignocellulosic biomass, requires upgrading to extent its application range and for instance to allow for co-feeding in an existing oil-refinery. Catalytic hydrotreatment reactions (350 °C, 20 MPa total pressure, and 4 h reaction time) with mono- and bi-metallic metal catalysts based on Rh, Pt, Pd on a zirconia support were performed in a batch set-up. Pd/ZrO 2 showed the highest activity, followed by Rh/ZrO 2. Upgraded oils with the best product properties were obtained with Rh/ZrO 2. For this catalyst, the TGA residue, which is a measure for coking tendency, was 13.4 wt% and the M w of the upgraded oil (748 g/mol) was lowest. All noble metal catalysts showed higher activities per gram of metal than the benchmark catalyst CoMo/Al 2O 3. Hydrotreatment reactions at variable batch times were performed to gain insights in reaction pathways and showed the involvement of competitive hydrogenation/hydrocracking and polymerisation pathways. Temperature programmed oxidation (TPO) measurements of spent catalysts showed the presence of carbonaceous deposits on the catalyst (2–6 wt%). These deposits may be removed by oxidation at temperatures lower than 600 °C without changing the morphology of the catalyst.

Support Effects on the Oxidative Dehydrogenation of Ethane to Ethylene over Platinum Catalysts

Oxidative dehydrogenation of ethane to form ethylene was carried out over a platinum catalyst at short contact times. Alumina, zirconia, or silica reticulated foams were used as catalyst supports. The carbon selectivity to form ethylene was affected by the support material whereas the conversion of ethane was not affected to a large extent. The selectivity to form ethylene decreased from silica, to alumina, to zirconia. The temperature programmed desorption of ammonia carried out on the support materials showed that the zirconia support had a higher concentration of acid sites than either alumina or silica. After coating the supports, hydrogen chemisorption on the used catalyst showed metal dispersion was highest on silica and lowest on zirconia. The much higher selectivity on silica and alumina as compared to zirconia is explained by the lack of acid sites that catalyze the decomposition of ethylene to carbon. The higher dispersion of platinum on silica versus alumina will lead to a decrease in platinum ...

One pot synthesis of menthol from (±)-citronellal on nickel sulfated zirconia catalysts

The one-pot synthesis of menthol from (±)-citronellal was carried out using two catalysts: nickel supported on sol–gel sulfated zirconia (Ni/ZrS) and nickel added during the synthesis of sulfated zirconia (NiZrS). The supported catalyst was prepared by impregnation of nickel on the sulfated zirconia support, whereas NiZrS was prepared by the co-gellation of nickel and the sulfated zirconia by the sol–gel method. Two sets of catalytic tests were carried out. In both tests the catalysts were previously treated in He stream. First, the liquid phase cyclization of (±)-citronellal was carried out with both ZrS and NiZrS catalysts. The results showed that both ZrS and NiZrS catalysts are highly active and selective towards isopulegols (100% of selectivity) and highly stereoselective towards (±)-isopulegol (∼70% of selectivity). A second reaction test was the synthesis of menthol. The catalysts were evaluated in a batch reactor at 1.4MPa of H2 and 100°C. The results showed that the catalysts allow to obtain a high catalytic activity and selectivity towards stereoisomers of menthol (100% selectivity of menthols) and a high selectivity towards (−)-menthol.

Precious metal catalysts in the clean-up of biomass gasification gas part 2: Performance and sulfur tolerance of rhodium based catalysts

Rh, Pt, and Pt-Rh catalysts on modified commercial zirconia support (m-ZrO 2) were screened for the clean-up of gasification gas from tar, methane, and ammonia both in the absence and presence of H 2S while varying the Rh metal content from 0.5 to 5 w-%. Our goal was to optimize the composition of the Rh/m-ZrO 2 catalyst in view of the production of ultra clean gas applicable for liquid biofuels synthesis. In the presence of 100 ppm sulfur, increasing Rh concentration from 0.5 to 5 w-% did not greatly improve the activity of the catalyst. The bimetallic Pt/Rh/m-ZrO 2 catalyst was also less active than the 0.5 w-% Rh/m-ZrO 2 catalyst. Furthermore, the Rh/m-ZrO 2 catalyst regained its performance at the set point of 800 °C when the sulfur feed was turned off even after exposures to 500–1000 ppm sulfur. Our data allow us to suggest that in the presence of sulfur, the active sites responsible for the reforming reactions are poisoned, but less impact occurs on sites responsible for oxidation reactions. Furthermore, the screening experiments allow to suggest that the Rh/m-ZrO 2 catalyst could be applicable to hot gas cleaning in the presence of sulfur (> 50 ppm) at above 800 °C using a moderate gas hourly space velocity of approximately 3400 1/h. Since biomass gasification gas generally contains sulfur, the 0.5 w-% Rh/m-ZrO 2 catalyst could be a promising option for gasification gas clean-up applications at temperatures above 800 °C where it reduces tar to very low levels.

Acid–base properties of niobium-zirconium mixed oxide catalysts for glycerol dehydration by calorimetric and catalytic investigation

The acid–base properties of fresh and used niobium-zirconium mixed oxide catalysts, used for the dehydration of glycerol to acrolein, have been characterized by various techniques. These techniques include ammonia thermo-programmed desorption (TPD), infrared spectroscopy of absorbed pyridine, and adsorption microcalorimetry of ammonia and sulfur dioxide. Relationships between the catalytic properties and the acid–base properties of fresh catalysts have been investigated. The most efficient catalysts were shown to be those for which the zirconia support had a better niobium oxide species covering, but no specific relationship could be established between the acid–base, and the selectivity to acrolein. Characterization of the used catalysts showed that the acidic properties of the catalysts had changed considerably with the time spent on stream. No further strong acid sites, and only weak or very weak acid sites were detected. A linear relationship between the total quantity of remaining acidic sites and the rate of glycerol conversion was determined, taking into account an intrinsic activity of the stronger sites, which is more than ten times that of the weaker ones. The deactivation of the catalysts as a function of time on stream has been related to the formation of cyclic molecules, produced by the reaction of acrolein with by-products resulting from the decomposition of hydroxyacetone and also possibly acrolein and glycerol.

Progress Toward Inkjet Deposition of Segmented-in-Series Solid-Oxide Fuel Cell Architectures

This paper presents our progress in applying inkjet-printing technology in fabrication of solid-oxide fuel cells (SOFCs) in the segmented-in-series architecture. Cell materials include a nickel anode, yttria-stabilized zirconia electrolyte, strontium-doped lanthanum manganate cathode, and lanthanum-doped strontium titanate interconnect. Inks are formulated from commercially sourced powders, and printed onto porous, chemically inert, partially stabilized zirconia supports. Accurate registration of SOFC materials is observed at a feature size of approximately 100 μm. After high-temperature sintering, good adhesion between SOFC materials and the support is also evident.

New efficient and long-life catalyst for gas-phase glycerol dehydration to acrolein

Zirconium and niobium mixed oxides have been shown to be selective catalysts for dehydration of glycerol to acrolein, at 300 °C in the presence of water. The catalysts exhibit a selectivity to acrolein of approximately 72%, at nearly total glycerol conversion. More selective catalysts have been designed for this reaction, but whereas all of these are almost completely deactivated after only 24 h, ZrNbO catalysts still exhibit 82% conversion efficiency after 177 h on stream, its acrolein selectivity remaining unimpaired. Catalysts have been characterized by various techniques, showing that active and selective sites are weak or moderately acid Brønsted sites, whose presence is related to that of polymeric niobium oxide species in interaction with the zirconia support. The key stability of the catalysts has been attributed to the neutralization of Lewis acid of uncovered zirconia, which are unselective coke initiator sites.

Precious metal catalysts in the clean-up of biomass gasification gas Part 1: Monometallic catalysts and their impact on gasification gas composition

The performance of Rh, Ru, Pt, and Pd on modified commercial zirconia support (m-ZrO 2) was compared to a benchmark Ni/m-ZrO 2 catalyst in the presence of H 2S in the clean-up of gasification gas from tar, methane, and ammonia. The aim was to produce ultra clean gas applicable for liquid biofuel production. In general, the activity towards the decomposition decreased in the order of aromatic hydrocarbons, ethylene > methane > ammonia. Hydrocarbon decomposition on m-ZrO 2 supported Rh, Ni, and Ru catalysts mainly occurred at 800–900 °C through reforming and/or dealkylation reactions. Aromatic hydrocarbon decomposition reactions proceeded on Pt/m-ZrO 2 and Pd/m-ZrO 2 via oxidation reactions at temperatures of 600–800 °C, while at 900 °C, the reforming and/or dealkylation reactions were dominating also on Pt/m-ZrO 2 and Pd/m-ZrO 2 catalysts. During longer test runs of ten hours at 800 °C, the activity of the Rh/m-ZrO 2 catalyst declined in the presence of 100 ppm H 2S due to the sulfur poisoning effects, coke formation, and the particle size growth. Although the performance of Rh/m-ZrO 2 declined, it still remained better than Ni/m-ZrO 2 both towards naphthalene and total aromatic hydrocarbon, while only Ni/m-ZrO 2 and Ru/m-ZrO 2 decomposed ammonia in the presence of sulfur. Nevertheless, the most promising catalyst for clean gas production was Rh/m-ZrO 2.

Steam reforming of ethanol over Ni/ZrO 2 catalysts: Effect of support on product distribution

Ni catalysts supported on ZrO 2 with different crystalline phases and particle sizes were prepared to study the role of zirconia support in ethanol steam reforming for hydrogen production. Catalytic behavior of the catalysts was examined at relatively low temperature of 673 K with different contact times. The decrease in particle size of zirconia results in enhanced metal-support interaction, which accounts for the high activity of the catalyst. Regarding the impact of crystalline phase of zirconia on catalytic performance, tetragonal zirconia yields a higher activity in water gas shift reaction but a lower activity in methane steam reforming than that of monoclinic zirconia. Nevertheless, zirconia plays a secondary role in product distribution, especially at long contact times. Catalytic activity tests performed at elevated temperature demonstrated a high activity and stability of Ni/ZrO 2 catalyst for hydrogen production from steam reforming of ethanol.

Mono and Bifunctional Catalysts for Styrene Oxide Isomerization or Hydrogenation

Styrene oxide can be effectively isomerized to phenyl-acetaldehyde (98%) over amorphous silica alumina catalysts under very mild liquid phase conditions. On the other hand, a copper catalyst prepared using a silica zirconia support gave up to 80% yield in the hydrogenation of styrene oxide to 2-phenyl-ethanol.

Hydrogen production from catalytic gasification of switchgrass biocrude in supercritical water

Biomass can be liquefied to produce biocrude for ease of transportation and processing. Biocrude contains oxygenated hydrocarbons of varying molecular structure and molecular weights, including lignin derived products, sugars and their decomposition products. In this work several catalysts were screened for hydrogen production by gasification of switchgrass biocrude in supercritical water at 600 °C and 250 bar. Nickel, cobalt, and ruthenium catalysts were prepared and tested on titania, zirconia, and magnesium aluminum spinel supports. Magnesium aluminum spinel was seen to be an inappropriate support as reactors quickly plugged. Ni/ZrO 2 gave 0.98 mol H 2/mol C, the highest hydrogen yield of all tested catalysts; however, over time, increase in pressure drop lead to reactor plugging with all zirconia supported catalysts. Titania supported catalysts gave lower conversions, however they did not plug during the course of the study. Charring of all catalysts was seen to occur at the entrance of the reactor as the biocrude was heated. All support materials suffered significant surface area loss due to sintering.

Improved photocatalytic activity of indium doped cadmium sulfide dispersed on zirconia

A novel composite photocatalyst of indium doped cadmium sulfide dispersed on zirconium oxide has been synthesized, which shows enhanced photocatalytic activity for hydrogen generation from water. In this system, cadmium sulfide exists as a separate dispersed phase on the zirconia support. Optical absorption spectra indicate a blue shift of absorption edge for CdS and In doped CdS dispersed on ZrO2 compared to pure CdS and indium doped CdS. Among the supported CdS, In doped CdS exhibits better optical absorption property. Photocatalytic studies for hydrogen generation from water show an enhanced activity for CdS dispersed on ZrO2 and indium doping in CdS enhances the activity further. Fluorescence lifetime studies indicate that, in the supported CdS, the charge carriers have higher lifetime than that in the unsupported CdS. Photocurrent response experiments show a relatively higher current output for the In doped CdS dispersed on ZrO2 support. The enhanced photocatalytic activity of this composite sample is attributed to a combination of factors like enhanced lifetime of the photogenerated charge carriers, increased photoresponse and improved surface area. The present study leads to a new observation that the photocurrent response and photocatalytic activity of CdS and indium doped CdS are enhanced when they are dispersed on a support like ZrO2. These composites with Pd as co-catalyst exhibit a large increase in the photocatalytic activity due to the increased availability of electrons on the metal surface by the interfacial transfer of electrons from CdS to Pd, when irradiated.

Hydrodeoxygenation of guaiacol: Part II: Support effect for CoMoS catalysts on HDO activity and selectivity

Bio-oils coming from ligno-cellulosic biomass are suitable material for the production of second generation biofuels. The oxygenated compounds have to be eliminated to confer good properties to these bio-oils and to permit their addition to traditional fuels. Hydrodeoxygenation (HDO) process which allows O-elimination by C–O bond cleavage under H2 can be realized with the same type of catalysts as those used in HDS, supported CoMoS or NiMoS phases. In this work, the support effect associated with CoMoS catalysts has been investigated in guaiacol HDO reaction. Zirconia and titania supports have been compared with the traditional industrially used γ-alumina and it appeared that zirconia as support gave very efficient conversion of guaiacol into deoxygenated hydrocarbons with a totally different selectivity. The difference in selectivity allowed us to propose a different reaction scheme compared to γ-alumina and titania supported CoMoS.