ZrO2 Catalysts Research Articles

Highly selective hydrogenation of CO2 to methanol over CuO–ZnO–ZrO2 catalysts prepared by a surfactant-assisted co-precipitation method

A series of CuO–ZnO–ZrO2 catalysts are synthesized by a surfactant-assisted co-precipitation method and tested for the synthesis of methanol from CO2 hydrogenation. The effects of calcination temperature on the physicochemical properties of as-prepared catalysts are investigated extensively by TG-DSC, N2 adsorption/desorption, XRD, N2O chemisorption, SEM/TEM, EDX, XPS, TPR, H2-TPD and CO2-TPD techniques. The results show that the size of copper particles increases with the increase in calcination temperature, leading to the decrease in turnover frequency (TOF) for methanol formation. Moreover, compared with the counterparts prepared by the conventional co-precipitation method, the CuO–ZnO–ZrO2 catalysts prepared by this novel method show significantly high methanol selectivity. The superior property of the prepared CuO–ZnO–ZrO2 catalyst can be attributed to the formation of more amounts of Cu–ZnOx and/or Cu–ZrOx species resulted from the homogeneous element distribution, intimate interface contact of Cu species with ZnO and/or ZrO2, and to porous structure with larger pore size.

Coking and deactivation of a mesoporous Ni–CaO–ZrO2 catalyst in dry reforming of methane: A study under different feeding compositions

Abstract A previously developed mesoporous Ni–CaO–ZrO 2 catalyst (NCZ) was submitted to dry reforming of methane (DRM), and the influence of feeding compositions on the properties of accumulated carbon was comprehensively studied. To this end, the used catalysts (NCZ- x ) were characterized with a particular focus on the carbon residuals, using X-ray diffraction, N 2 adsorption, transmission electron microscope, scanning electron microscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy, etc. The results indicate that by varying the composition of the feeding gas, the morphology and chemical inertness of the accumulated carbon changed considerably, and the deactivation of the NCZ catalyst under CH 4 -rich conditions can be associated with the formation of coating carbon species that leads to the coverage of highly active Ni nano particles (NPs).

Conversion of isobutane-butenes mixtures on H-USY and SO 4 2− /ZrO2 catalysts under supercritical conditions: Isobutane alkylation and butenes oligomerization

The conversion of isobutane-butenes mixtures on the H-form of ultrastable zeolite Y and sulfated zirconia under supercritical conditions at 150–160°C and 80 atm was studied. The isobutane/C4-olefins molar ratios (I/O) were 1.5, 14, and 28. In isobutane alkylation (I/O = 14 and 28), sulfated zirconia was more stable: at 150°C and 80 atm, the olefin conversion above 90% was retained for 5 h. Under the same conditions, the deactivation of the zeolite catalyst started after 1–2.5 h (depending on the initial I/O ratio). Selectivity for the formation of C8 hydrocarbons was 30–40%. An increase in the butene content of the initial mixture led to the domination of the dimerization of butenes over the alkylation of isobutane.

Towards conversion of octanoic acid to liquid hydrocarbon via hydrodeoxygenation over Mo promoter nickel-based catalyst

In the current paper, Mo doped Ni–ZrO2 catalyst was prepared, which was used for the liquid hydrocarbon from conversion of octanoic acid via hydrodeoxygenation (HDO). The experimental results showed that the reaction product is mainly C8 alkane with a yield of 77.07% when 10Mo/Ni–ZrO2 was used as the catalyst compared with the major product of C7 alkane over Ni–ZrO2 catalyst with a yield of 69.68%. The introduction of Mo into the Ni–ZrO2 channel generated in Mo/Ni–ZrO2 samples was characterized by nitrogen sorption, TEM, XRD, TPR, and TPD. The results demonstrated that the doping Mo particles to the Ni–ZrO2 catalyst resulted in the transformation of ZrO2 support from cubic form (c-ZrO2) to monoclinic form (m-ZrO2), and the improvement of the hydrogen adsorption capacity and acid property of the catalyst. Thus, the doping of Mo favored the dehydration–hydrogenation reactions of octanol intermediate which in turn facilitated octanoic acid HDO to C8 alkane. Therefore, a novel approach to octanoic acid HDO to C8 alkane is introduced, which provides a basis as well as technical parameters for its further industrialization.

Copper–gallia interaction in Cu–Ga2O3–ZrO2 catalysts for methanol production from carbon oxide(s) hydrogenation

The impact of the interaction between copper and gallia was studied over a selected set of supported (2wt%) Cu on Ga2O3, ZrO2 and Ga2O3–ZrO2 catalysts, which were employed in the methanol synthesis from CO2 and CO mixtures. The higher initial rate of methanol production on the Cu/ZrO2 catalyst was accompanied by an activity loss of ∼35% after 5h on stream. However, all the gallated catalysts were notoriously more stable (and selective) than copper on pure zirconia was. Temperature-programmed reduction in H2, X-ray photoelectron spectroscopy and infrared spectroscopy of adsorbed CO results proved that temperatures higher than 553K are needed to completely reduced Cu2+ to metallic Cu particles in the gallia-containing catalysts, which was attributed to the formation of a CuGa2O4 nanospinel. The ternary Cu–Ga2O3–ZrO2 catalysts showed an intermediate behavior, quite dependent on the preparation protocol, which emphasizes the need for tuning the degree of Cu–oxides interactions. It is suggested that just a moderate copper–gallia interaction is beneficial in terms of both activity and selectivity but, also, that a detrimental loss of ‘active’ copper should be avoided.

Catalytic Conversion of Levulinic Acid and Its Esters to γ-Valerolactone over Silica-Supported Zirconia Catalysts

Abstract Levulinic acid and its esters, important intermediate chemicals produced from biomass resources, were converted to γ-valerolactone via a catalytic transfer hydrogenation process over silica-supported zirconia catalysts. Silica support with a higher surface area provided highly dispersed active zirconium oxide species, which exhibited superior catalytic activity to the conventional ZrO2 catalyst.

Aluminum‐Doped Zirconia‐Supported Copper Nanocatalysts: Surface Synergistic Catalytic Effects in the Gas‐Phase Hydrogenation of Esters

AbstractThe efficient gas‐phase selective hydrogenation of a series of esters to the corresponding alcohols was achieved over well‐dispersed aluminum‐doped zirconia‐supported copper nanocatalysts (Cu/Al‐ZrO2), which were prepared through a homogeneous coprecipitation route in the presence of cetyl trimethyl ammonium bromide. The characterization revealed that the structure and catalytic performance of Cu/Al‐ZrO2 nanocatalysts were profoundly affected by the addition of Al. Compared with the Al‐free catalyst, Al‐doped materials had higher specific surface areas and smaller copper nanoparticles. In particular, the results confirmed that the incorporation of Al into the ZrO2 framework could form tetrahedrally coordinated Al3+ species, leading to the improvement of metal dispersion and the formation of more surface Lewis acid sites. In the gas‐phase selective hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG), 100 % DMO conversion, 97.1 % EG selectivity, and a high turnover frequency of 16.9 h−1 were achieved over Cu/Al‐ZrO2 catalyst with a Al/(Cu+Zr+Al) mass ratio of 0.1. The high efficiency of Cu/Al‐ZrO2 catalysts in DMO hydrogenation was attributed mainly to the surface synergistic catalytic effect between highly dispersed metallic copper species and strong Lewis acid sites, which promoted the hydrogenation reaction related to the ester groups, unlike the single case of Cu+Cu0 synergy reported previously that was found to control the extent of hydrogenation. The obtained catalysts displayed excellent catalytic performance in the gas‐phase hydrogenation of other esters including dimethyl succinate, dimethyl maleate, dimethyl adipate, and 1,4‐cycolhexane dicarboxylate.

Spectroscopic characterization of CuOx/TiO2–ZrO2 catalysts prepared by a-step sol–gel method

Copper–titania–zirconia mixed oxides with TiO2/ZrO2 1:1 atomic ratio and copper content of 1, 3 and 5wt% were prepared by one-step sol–gel method. X-ray diffraction and gas-volumetric analysis showed poor crystallinity and high specific surface area (around 250m2/g) of the catalysts calcined at 400°C. The nature of the copper species in the mixed oxides was characterized by temperature-programmed reduction in hydrogen (TPR), low-temperature electron paramagnetic resonance (EPR) and diffuse reflectance (DR) UV–Vis spectroscopies. These techniques suggested the presence of different copper species including distorted octahedral Cu2+ ions (isolated or quasi-isolated) in the solid solution bulk, characterized by a TPR peak above 400°C (labeled as T1), electronic d–d transitions around 800nm and an anisotropic EPR signal with two hyperfine interactions in the g|| region. The symmetry of this site changed from rhombic (S1) to axial (S3) while increasing copper loading. The inclusion of copper ions in the TiO2–ZrO2 matrix was also testified by changes in the mixed-oxide edge position. Two families of supported copper oxide were found. CuO “bulk-like” showed relatively high reduction temperature (T2, around 250°C), while highly dispersed CuOx nanoparticles/clusters resulted in TPR peaks around 170 and 200°C (T4 and T3). These species were responsible for the UV–Vis adsorption above 400nm and for the broad and asymmetric axial EPR signal with g|| in the range from 2.14 to 2.29 (S2 and S2′). Finally, 2-propanol decomposition was employed as a test reaction to probe the catalyst's surface properties. The results suggested a marked effect of copper loading on the reactivity pattern, confirming the presence of CuO/CuOx particles on the surface of the TiO2–ZrO2 support.

Catalytic Non-Thermal Plasma Decomposition of Ethylene by Using ZrO2Nanoparticles

In the present work, ZrO2 nanoparticles loaded on glass wool (GW) were employed for catalytic and plasma-catalytic decomposition of ethylene. Unlike ZrO2 pellets, nanosized ZrO2 was found to exhibit catalytic activity for the decomposition of ethylene. Some carbon-containing by-products like CH4, C2H2, and HCHO were detected under room-temperature operation of the reactor. The formations of such unwanted by-products were suppressed and the conversion into CO2 was enhanced when the ZrO2 catalyst was combined with non-thermal plasma at high temperatures. The nanosized ZrO2 exhibited a stable decomposition performance during 80-h continuous operation, suggesting that it is able to withstand deactivation without substantial loss in its catalytic activity.

Interaction of H2S with ZrO2 and its influence on reactivity of surface oxygen

ZrO2 catalysts can be efficiently applied to convert tars into less harmful compounds in biomass gasification gas clean-up, also in the presence of H2S. In fact, H2S has even been observed to enhance naphthalene (a model compound for tar) oxidation activity on ZrO2. Sulfur binding and its effect on the reactivity of surface oxygen species, including OH groups as well surface lattice oxygen, on ZrO2 was studied using temperature-programmed methods. At 30°C approx. half of the adsorbed H2S was physisorbed and the other part dissociated titrating terminal OH groups. This dissociated H2S was strongly adsorbed. Moreover, it was found that after treatment with H2S until 400°C half of the adsorbed species were irreversibly adsorbed. H2S adsorbed inducing desorption of water at two distinct temperatures (∼170 and 280°C) during temperature ramp. Thus, H2S adsorption at elevated temperatures produced surface sulfur by replacement of surface lattice oxygen at two types of minority sites (max. 5% of a monolayer). Therefore we suggest that multicoordinated OH groups and surface lattice oxygen at defective sites are involved. CO-TPR revealed increased reactivity of surface lattice oxygen on ZrO2 with increasing amount of sulfur on the surface. In addition, strong adsorption of carbonates was suppressed by the presence of sulfur. The observed H2S-induced enhancement of naphthalene oxidation in gasification gas clean-up is suggested to be caused by the increased reactivity of surface oxygen species in the vicinity of sulfur species on the surface.

High-yield selective conversion of carbohydrates to methyl levulinate using mesoporous sulfated titania-based catalysts

Mesoporous sulfated-metal oxides and mixed-metal oxides prepared by a facile coprecipitation method employing titanium oxysulfate–sulfuric acid complex as a precursor of both titanium and sulfate are highly active and selective for direct methanolysis of carbohydrates to methyl levulinate. The most active sulfated TiO2–ZrO2 catalyst selectively converted fructose to methyl levulinate with a remarkably high yield (71%) after 1h at 200°C. Significant amounts of methyl levulinate were also obtained from sucrose (54%) and glucose (23%) after 1h at 200°C. The used catalyst was easily recovered and recycled without any loss of selectivity although activity decreased due to humin deposition on the surface. The spent catalysts were easily rejuvenated through calcination in air. The formation of ethers during dehydration was negligible suggesting that methanol can be recycled after distillation.

Nanostructured Ce0.7Mn0.3O2−δ and Ce0.7Fe0.3O2−δ solid solutions for diesel soot oxidation

Nanostructured Ce0.7Mn0.3O2−δ (CM) and Ce0.7Fe0.3O2−δ (CF) solid solutions were prepared by a facile coprecipitation method and evaluated for soot oxidation. The structural, morphological, and surface properties were investigated by various techniques, namely, XRD, ICP-OES, BET surface area, SEM-EDX, TEM-HRTEM, UV–vis DRS, Raman, FT-IR, XPS, H2-TPR, and TGA-DTA. XRD and TEM results confirmed formation of nanocrystalline solid solutions with the incorporated Mn and/or Fe cations in the ceria lattice. SEM studies ensured nanoparticle nature of Ce–Mn–O and Ce–Fe–O solid solutions with homogeneous distribution. ICP-OES and EDX analysis confirmed actual amount of metal loadings in the respective catalysts. UV–vis DRS and Raman results revealed the formation of more oxygen vacancies, which lead to the creation of more surface active species (Ce4+/Ce3+ and O*). XPS results revealed that the doping of Mn and/or Fe into the ceria lattice makes some Ce4+ transferred into Ce3+ in order to maintain the electrical neutrality, thereby facilitate the reduction of Ce4+→Ce3+ and the formation of oxygen vacancies. TPR results showed that the mixed oxides reduce at lower temperatures than pure ceria. This observation confirmed that there is a synergetic interaction between Ce–O and M–O (M=Mn, Fe). The catalytic activity of CM and CF samples towards soot oxidation has been evaluated under tight contact conditions and compared with the well-established CeO2–ZrO2 (CZ) catalyst. Among the investigated catalysts, the Mn and/or Fe doped ceria solid solutions showed improved catalytic activity. The order of activity is as follows: CM>CF>CZ>C. Further, the CM and CF catalysts were found to be thermally quite stable compared to pure ceria. In particular, the CM sample exhibited superior catalytic activity (T50=∼665K) and thermal stability towards soot oxidation.

Synthesis and Structural Characterization of Eu2O3 Doped CeO2: Influence of Oxygen Defects on CO Oxidation

In this study, nanosized Ce0.9Eu0.1O2−δ (CE 91) and Ce0.8Eu0.2O2−δ (CE 82) solid solutions were prepared by a modified co-precipitation method, followed by calcination at 773 and 1,073 K. Structural properties of the prepared materials were thoroughly investigated by different characterization techniques, namely, X-ray powder diffraction (XRD), Brunauer–Emmett–Teller surface area, high resolution transmission electron microscopy, Raman spectroscopy, UV–Visible diffuse reflectance spectroscopy (UV–Vis DRS), and X-ray photoelectron spectroscopy (XPS). The catalytic activity for CO oxidation was assessed and compared with the well-established CeO2–ZrO2 (CZ) catalyst. As confirmed by powder XRD, the synthesized materials maintain the F-type crystalline structure characteristic of ceria (CeO2). The interaction of CeO2 with Eu3+ dopant promoted the formation of oxygen vacancies as revealed by Raman results. UV–Vis DRS and XPS data suggest that Ce exists in both 3+ and 4+ oxidation states and Eu in the 3+ state. Results of catalytic CO oxidation indicate that Eu doped ceria exhibits a better performance than Zr doped ceria irrespective of the calcination temperature. This may be due to the increased number of oxygen defects and the easily reducible nature of the material, which results from the substitution of Ce4+ species with Eu3+ ions.

Catalytic Performance of Brønsted and Lewis Acid Sites in Phenylglyoxal Conversion on Flame‐Derived Silica–Zirconia

AbstractFlame‐derived silica–zirconia has been used for the promising one‐step catalytic conversion of phenylglyoxal (PG) to mandelates, important intermediates in pharmacy and fine chemistry. In the literature it was proposed that Lewis acid sites (LAS) on solid acids promote mandelate production, whereas Brønsted acid sites (BAS) only generate acetal byproducts during PG conversion. Herein it is shown that ZrO2, which contains only LAS and no BAS, exhibits a very low activity for PG conversion to afford a yield of mandelate of only 8 % after 6 h. The activity of this ZrO2 catalyst was confirmed by the condensation of acetone, in which its LAS could activate the carbonyl groups immediately for the fast condensation of all acetone molecules. The introduction of BAS by the admixing of silica precursor to the feed in the flame‐spray pyrolysis enhanced the yield of mandelate up to 52–67 %. This indicates that BAS are mainly responsible for the PG conversion to mandelate on silica–zirconia catalysts and that their LAS are nearly inactive for this reaction.

Zirconia-Supported Copper and KNO3 Catalysts for Diesel Soot Combustion. Deactivation by Hydrotreatment and SO2

In this study, the sulfur tolerance and hydrothermal stability of Cu-KNO3/ZrO2 catalysts in catalytic diesel soot oxidation were investigated. Supported alkaline nitrate catalysts have shown excellent activity for soot oxidation in the presence of O2 or NO/O2. High-temperature water vapor treatments do not affect the catalytic activity, suggesting a good hydrothermal stability of the catalysts. Treatments performed at high SO2 concentration lead to a partial deactivation of the catalysts for the combustion reaction in the presence of O2. The presence of copper improves the sulfur tolerance of the KNO3/ZrO2 catalyst for the combustion of soot in the presence of NOx. NO/O2 present in the feed flow of the reactor can regenerate in situ nitrate anions that provide the redox cycles required for the reaction. Keywords: Diesel soot, Combustion, Hydrothermal stability, SO2.

Evaluation of Zr–Alumina in Production of Polyoxymethylene Dimethyl Ethers from Methanol and Formaldehyde: Performance Tests and Kinetic Investigations

Polyoxymethylene dimethyl ethers (PODEn) converted from methanol and formaldehyde were investigated with alumina supported ZrO2 catalyst in a stainless steel tube fixed-bed reactor within the temperature range from 333 to 433 K and the pressure range from 0.1 to 2.5 MPa. First, results from catalytic performance tests showed that the catalyst γ-Al2O3 containing 4 mol % ZrO2 exhibited the highest activity for PODEn synthesis. The stoichiometry analysis of raw material indicated that ZrO2 modified catalyst had the optimum activity at methanol/formaldehyde = 3 (mol/mol). An increase of the reaction pressure resulted in a significant increase in methanol conversion from 13.18 to 48.64%, and selectivity to PODE3–8 was enhanced to 24.82%. The temperature experiment analysis confirmed the optimization of the reaction temperature to be 393 K. Second, SEM and TEM showed the relationship between the catalytic activity and the catalyst-crystal alignment. Incorporation of ZrO2 in the framework of γ-Al2O3 was noticed ...

Hydrogen storage performance of 2LiH + MgB2 doped with hydrothermal-synthesized ZrO2 nanorods

In this study, we synthesized ZrO2 nanorods through a hydrothermal process as a catalyst precursor for the reversible hydrogen storage reaction between 2LiH + MgB2 and 2LiBH4 + MgH2. The 2LiH + MgB2 composites doped with the ZrO2 nanorods demonstrated superior and stable hydriding/dehydriding kinetics upon cycling. The XRD, SEM and HRTEM results revealed that the doped ZrO2 nanorods were transformed into ZrB2 nanoparticles with a size of a few nanometers during the first hydrogenation. The initial nanosize of the ZrO2 catalyst precursor accounted for the formation of extremely fine ZrB2 nanoparticles, which acted as heterogeneous nuclei of MgB2. The present study provides a new route for performance enhancement of complex hydride composites through manipulating the nanostructure of catalysts.

Oxygen Reduction Reaction Sites and Electron Conduction Mechanism of Zr-Oxide-Based Catalyst:Soft X-Ray SR-XPS and First-Principles Calculations

Polymer electrolyte fuel cells (PEFCs) have expected as one of the key energy devices in future sustainable society. PEFCs, however, have difficult issues such as insufficient oxygen reduction reaction (ORR) activity and expensive Pt consumption. To overcome such difficulties, various non-platinum ORR catalysts, such as, carbide, nitride, and oxide were examined as alternative of Pt [1]. Among them, Zr oxide-based catalysts attract much attention. Such transition-metal-oxide catalysts show the high ORR onset potentials, but ORR current is very low. Thus, identifying the ORR sites, and designing surface structure to have effective ORR sites, is mail issues in developing oxide-base catalysts.Previously, we reported that oxygen-vacancy sites could be ORR sites by surface-sensitive conversion-electron-yield x-ray absorption spectroscopy (CEY-XAS) [2]. But we still lack detailed information on preferable electronic structure of oxide-base ORR catalyst. Since carbon is deposited at catalysts surface during partial oxidation preparation processes, conventional laboratory XPS does not provide effective information, especially at valence band (V.B.) region. Thus, we conducted highly brilliant soft X-ray synchrotron radiation (SR)-XPS measurements. First-principles calculation was adopted to interpret the partial density of state (PDOS) of V. B.ZrO2 based catalyst samples were prepared under O2 and H2/N2 atmosphere from Zr- phthalocyanine. The SR-XPS measurements were performed on BL-18A beam line at Photon Factory (PF) of High Energy Accelerator Research Organization (KEK). PDOS calculation was carried out by using the plane-wave basis projected augmented wave (PAW) method (VASP) [3].Figure 1 (a) shows the soft x-ray SR-XPS spectra of ZrO2 reference. Each spectrum was obtained after subtracting the spectrum measured at 31 eV X-ray energy. We can see that peak intensity at 4 to 8 eV regions were increased as incident energy increased, suggesting that these peaks originate from ZrO2. As shown in Fig.1 (b), the SR-XPS spectra of ZrO2 catalyst also show similar trend. This indicates that we can truly observe V.B of catalysts even if a part of surface is covered with carbon. Figure 2 shows the PDOS spectra calculated ZrO2 with oxygen vacancy. The Peak near 4eV can be originated from O 2p. This result suggest reduction of SR-XPS spectral intensity for catalysts compared with reference ZrO2comes from oxygen vacancy in the catalysts, and such O-vacancy should play a role in emergence of ORR activity. Detailed electronic structure consideration will be presented at Meeting. Acknowledgement: A part of this work was performed under the “Non-precious metal oxide-based cathode for PEFC Project” supported by the New Energy and Industrial Technology Development Organization (NEDO). SR-XPS measurements were performed with an approval of High Energy Accelerator Research Organization (Proposal No. 2013P102) .

Bulk and surface characterization and isomerization activity of Pt/WO4 2−/ZrO2 catalysts of different preparations

The texture, phase and surface composition and acidity of impregnated and precipitated Pt/WO4 2−/ZrO2 catalysts have been investigated with XRD, XPS, FTIR spectroscopy, and BET measurements. It has been shown that increasing the tungstate ion concentration in hydrated zirconium oxide results in an increase in the t-ZrO2 fraction in the catalysts following high temperature activation. While a fraction of W6+ and W5+ cations forms a solid solution with zirconia, the remaining W ions are stabilized on the catalysts surface as (–WOx–)n clusters. The catalytic activity in n-heptane isomerization seems to correlate with catalyst surface acidity to reach the greatest value at the WO4 2− concentration in the range of 12.9–17.6 mol %.

Effects of ZrO2 on the Nitridation Behavior and Mechanical Properties of Reaction-Bonded Si3N4/h-BN Composite

This paper presented a rapid nitridation route to fabricate reaction-bonded Si3N4/h-BN ceramic composite by the addition of ZrO2. The effects of ZrO2 on the silicon nitridation behavior, microstructure, and mechanical properties of the composite were investigated. The results showed that ZrO2 could effectively promote the nitridation of silicon and significantly influence the microstructure and mechanical properties of the composite. The best nitridation result, almost full conversion, was achieved when the ZrO2 content was 8 wt.%, and the outstanding mechanical properties were also exhibited at this condition. TG-DTA and thermodynamic analyses revealed that the inter-conversion between ZrO2 catalyst and ZrN metastable phase could effectively inhibit microzone melting of silicon and make the fresh surfaces of silicon particles exposed to nitrogen, and consequently accelerated the nitridation of silicon.