ZrO2 Support Research Articles

Propylene epoxidation by oxygen over tungsten oxide supported on ceria-zirconia

Ce0.05Zr0.95O2 (denoted as CZ) was prepared by using a precipitation method to support tungsten oxide. For comparison, ZrO2 (denoted as Z) and CeO2 (denoted as C) supports were also prepared with the same method. The WOx/Z, WOx/CZ, and WOx/C catalysts were characterized by XRF, nitrogen adsorption–desorption, FE-SEM, SEM-EDX, XRD, Raman, H2-TPR, NH3-TPD, and CO2-TPD analyses. Propylene epoxidation by oxygen was carried out over WOx/Z, WOx/CZ, and WOx/C catalysts in a continuous flow reactor. In the propylene epoxidation by oxygen, WOx/CZ catalyst showed the desirable conversion of propylene (3.8%) and selectivity for propylene oxide (46.8%). Such superior catalytic performance of WOx/CZ catalyst compared to the other catalysts (WOx/Z and WOx/C) was attributed to the moderate reduction ability and the optimum ratio of acidity/basicity.

Use of ZrO2 supported on bamboo leaf ash as a heterogeneous catalyst in microwave-assisted biodiesel conversion

In this research, bamboo leaf ash was utilized as ZrO2 support for heterogeneous catalyst application. The preparation of ZrO2-supported bamboo leaf ash (ZrO2/BLA) was conducted by the impregnation method with a metal content of 20%wt. The physicochemical characterization of the prepared material was studied using XRD, gas sorption analysis, FTIR and SEM-EDX. The material was tested for use in the biodiesel conversion of soybean oil under microwave-assisted conversion. The results show that the physicochemical characteristics of ZrO2/BLA facilitated the catalytic activity in biodiesel conversion. The effects of the reaction method, the methanol-to-oil molar ratio, and the catalyst weight were investigated. The microwave-assisted method gave yields comparable to those obtained via the reflux method in less time. The optimized conditions of fatty acid methyl ester (FAME) production using the microwave-assisted reaction method were a 15:1 methanol-to-oil molar ratio, 30 min of reaction time and 12%wt. catalyst weight. The catalyst exhibited reusability properties, as indicated by its relatively similar yields, initial rates and turnover frequencies observed when fresh and reused catalysts were used.

Effect of Si-modified zirconia on the properties of MoO3/Si-ZrO2 catalysts for sulfur-resistant CO methanation

A series of Si-modified ZrO2 supports were prepared by incorporating different content of silicon and loaded 25 wt.% MoO3 for sulfur-resistant CO methanation reaction. The prepared catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), N2 physisorption measurements, infrared spectra of adsorbed pyridine (Py-IR) and hydrogen temperature-programmed reduction (H2-TPR). The results demonstrated that Si-modified ZrO2 achieved more stable ZrO2 phase, more oxygen vacancies, larger specific surface area and more Brønsted acid sites. Catalysts prepared by modified ZrO2 exhibited smaller metal particles and different interaction between metal and support, which possessed higher activity with 63.4% CO conversion and 59% CH4 selectivity than unmodified catalyst at 550 °C under 2.5 MPa with 100 ppm H2S.

Methane decomposition into COx-free hydrogen and carbon nanomaterials over ZrO2–M (M = MgO, Al2O3, SiO2, La2O3 or CeO2) binary oxides supported cobalt catalysts

Hydrogen production via methane decomposition has attracted great attention as a source of clean energy. In this work, the catalytic decomposition of undiluted methane into COx-free hydrogen and carbon nanomaterial over ZrO2–M (M = MgO, Al2O3, SiO2, La2O3 and CeO2) binary oxides supported Co catalysts was studied. The fresh and spent catalysts were characterized by XRD, H2-TPR, N2 adsorption–desorption, TEM and Raman spectroscopy. The results revealed that the incorporation of secondary oxide to ZrO2 support played a vital role in the activity and stability of cobalt metal. The activity results illustrated that Co/Zr–Mg exhibited better activity in terms of hydrogen yield compared with the other Zr–M supported catalysts. This is ascribed to the moderate cobalt oxide-support interaction and forming CoMgOx species which enhance the Co3O4 dispersion and prevent its aggregation on the catalyst surface. On the other hand, the Co/Zr–Si catalyst showed the lowest activity due to the agglomeration of Co3O4 on the surface of the SiO2 support. High-resolution TEM images illustrated that almost the deposited carbon on the surface of spent catalysts was in the form of multi-walled carbon nanotubes.

Effect of reflux digestion time on MoO3/ZrO2 catalyst for sulfur-resistant CO methanation

A series of ZrO2 supports were treated by ammonia solution with different reflux digestion time, and loaded 25 wt% MoO3 for sulfur-resistant CO methanation reaction by incipient-wetness impregnation method. The MoO3/ZrO2 catalysts were also characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), infrared spectra of adsorbed pyridine (Py-IR). Compared to the undigested ZrO2, ZrO2 with reflux digestion in ammonia solution could achieve more oxygen vacancies, less Lewis acidic sites, smaller crystalline MoO3 and more amount of active sites. Generally, when the support reflux digested in ammonia solution exceed 12 h, the CO conversion of digested catalysts Mo/A-ZrO2-xh reached 60%, while the CO conversion of undigested catalysts was just 36% at the same reaction condition.

Study of the influence of the Cu/Ce loading ratio in the formation of highly active species on ZrO2 supported copper-ceria catalysts

This work studies the effect of different Cu/Ce loading ratios in the formation of highly dispersed copper species being interacting with CeO2 on zirconia-supported CuOCeO2 catalysts. These species have a strong effect on the CO oxidation reaction and for this reason such reaction was selected to conduct the present study. Catalysts with different metal loads were prepared by the co-impregnation method of Cu and Ce nitrates on ZrO2 support. It was found that the influence of the two metals occurs cooperatively. The type of copper species formed on the ZrO2 support depends on the Cu and Ce loads, with the existence of an optimum in activity when the Cu/Ce loading ratio being around 0.5. The incorporation of CeO2 increases the dispersion capacity of ZrO2 and facilitates the reduction of surface CuO species. Maintaining the Cu/Ce loading ratio constant at the optimal ratio (0.5) and increasing the total metal load (Cu+Ce) gave no significant increase in the catalytic activity above 6%. The latter suggests that higher metal loadings (Cu+Ce) does not lead to an increment of highly dispersed copper species interacting with CeO2, which is the most active species on the surface of this catalysts.

Insight into the effects of the oxygen species over Ni/ZrO2 catalyst surface on methane reforming with carbon dioxide

Carbon deposition on the catalyst surface has been considered as one of the main reasons to cause Ni catalyst deactivation during methane reforming with carbon dioxide (DRM). Generally, it is thought that the properties and levels of coke formation are significantly affected by the ability of CO2 adsorption and activation, which is closely related to the oxygen species over catalyst surface. In this study, the effects of oxygen species on the DRM over Ni/ZrO2 catalysts were investigated. Wherein, ZrO2 support was further treated under H2, N2, and O2 atmospheres respectively to obtain different oxygen species distribution over the surface, and 3 wt.% Ni was introduced by the deposition-precipitation method. The representative samples were characterized using XRD, EPR, XPS, FTIR, TPR, TPD, TPSR, TG, Raman and TPH techniques, etc. It was found that the treatment to ZrO2 in the reducing gas such as H2 was able to promote the formation of adsorbed oxygen species over the surface. CO2DRIFTS and CH4-TPSR experiments further confirmed that adsorbed oxygen species were favorable for enhancing both CO2 adsorption and activation and CH4 dissociation. As a result, the catalyst with more adsorbed oxygen species exhibited relatively outstanding performance for the DRM and promotional ability in removal of the deposited carbon.

Performance of a Ni/ZrO2 catalyst in the steam reforming of the volatiles derived from biomass pyrolysis

The activity and stability of a Ni/ZrO2 catalyst have been studied in a continuous bench scale plant, in which biomass has been pyrolysed at 500 °C in a conical spouted bed reactor and the outlet volatile stream has been subjected to catalytic steam reforming at 600 °C in a fluidized bed reactor. The influence of space time has been analyzed, and both the fresh and the deactivated catalysts have been characterized by means of different techniques: N2 adsorption-desorption, X-ray fluorescence (XRF), X-ray powder diffraction (XRD), temperature programmed oxidation (TPO), and transmission electron microscopy (TEM). The aim of this characterization is to relate catalyst performance to the evolution of the properties from the fresh to the deactivated catalysts. Thus, an increase in space time leads to an improvement in the stability of the catalyst extending its operation period from 20 to 100 min on stream, with a maximum H2 yield of 92.4% (referred to the maximum allowed by stoichiometry) when a space time of 20 gcat min gvolatiles−1 has been used. Although the ZrO2 support has suitable properties, coke deposition is the main cause of catalyst deactivation.

Engineering Stable Surface Oxygen Vacancies on ZrO2 by Hydrogen-Etching Technology: An Efficient Support of Gold Catalysts for Water-Gas Shift Reaction.

The surface structure of supports is crucial to fabricate efficient supported catalysts for water-gas shift (WGS). Here, hardly reducible ZrO2 was etched with hydrogen (H), aiming to modify surface structures with sufficient stable oxygen vacancies. After deposition of gold species, the obtained khaki ZrO2-H notably improved WGS catalytic activities and stabilities in comparison to the traditional white ZrO2. The characterization results and quantitative analysis indicate that sufficient surface oxygen vacancies of ZrO2-H support give rise to more metallic Au0 species and higher microstrain, which all boost WGS catalytic activities. Furthermore, optoelectronic properties were successfully used to correlate with their WGS thermocatalytic activities, and then a modified electron flow process was proposed to understand the WGS pathway. For one thing, the introduction of surface oxygen vacancies narrowed the band gap of ZrO2 and decreased the Ohmic barrier, which facilitated the flow of "hot-electron". For another thing, the conduction band electrons can be easily trapped by oxygen vacancies of ZrO2 supports, and then these trapped electrons immediately take part in reduction of H2O to H2. Thus, the electron recombination was suppressed and the WGS catalytic activity was improved. It is worth extending H2-etching technology to improve other thermocatalytic reactions.

Influence of preparation method and doping of zirconium oxide onto the material characteristics and catalytic activity for the HDO reaction in nickel on zirconium oxide catalysts

Different Ni/ZrO2 catalysts were prepared and tested for the hydrodeoxygenation (HDO) reaction of guaiacol. It was shown that the preparation mode of the ZrO2 support has a significant influence on the catalytic results, as remaining elements like Si and Na from the preparation can change the material properties. The influence of Si and Na onto these material properties, which were especially surface acidity and oxygen vacancy concentration, could be clarified. It could be also rationalized, how the change of these properties affects the results of the HDO reaction. Furthermore, it was demonstrated that the oxygen vacancy concentration is an important factor for the catalytic performance, although this property has hardly been considered in the design of HDO catalysts so far. La doping was found to be an efficient strategy to tune the oxygen vacancy concentration, and by using this approach the catalytic performance of the catalyst could be improved remarkably.

Enhanced catalytic activity of Ni–Mo2C/La2O3–ZrO2 bifunctional catalyst for dry reforming of methane

A series of Ni-modified Mo2C catalysts with La2O3-stabilized ZrO2 supports were synthesized via template method coupled with incipient wetness impregnation and temperature-programmed carbonization. The catalyst was tested in dry reforming of methane (DRM) reaction at the temperature range from 973 to 1173 K in a fixed-bed quartz reactor under atmospheric pressure. XRD, Raman, BET, H2-TPD, SEM, EDS and TEM were conducted to characterize the phase constitution, the pore structure, the morphology and the crystal structure of the catalysts. Ni–Mo2C nanoparticles of ~ 3 nm diameter were obtained for these catalysts, and the La2O3–ZrO2 supports exhibited a cubic lattice structure with a sheet shape, which is believed to contain an abundant of oxygen vacancies. And the synergistic interaction between the oxygen vacancy in La–Zr–O solid solution and the Ni–Mo2C particles could decrease the apparent activation energy of CO2. Both of them are beneficial for accelerating DRM reaction. CH4 conversion of the best specimen catalyst reaches 94% at 1173 K, and the catalyst maintains its stability after 100-h reaction. The superior catalytic activity of NMLZ-7.5 is attributed to the improved BET surface area (33.2 m2/g), smaller crystallites, grain boundaries and oxidation–carbonization cycle of Ni–Mo2C.

Ordered mesoporous Cu–Ca–Zr: A superior catalyst for direct synthesis of methyl formate from syngas

It is still a big challenge to obtain both highly active and stable Cu-based catalysts for direct synthesis of methyl formate (MF) from syngas. To address the issue, we have designed and synthesized a series of ternary Cu–Ca–Zr catalysts, namely, the ordered mesoporous Cu–Ca–Zr catalyst prepared by one-pot evaporation-induced self-assembly (EISA) method, and the supported CuO/CaO–ZrO2 catalysts by impregnating with copper precursor or by immobilizing copper nanoparticles. In the latter two catalysts, the ordered mesoporous CaO–ZrO2 support was also prepared by the EISA method. The catalysts were characterized by techniques such as ICP, XRD, TEM, N2 isotherm adsorption-desorption, XPS and H2-TPR, and used for direct synthesis of MF. The results indicated that the catalyst prepared by one-pot EISA method, in which the CuO species are highly dispersed in frame of CaO–ZrO2, exhibits much better activity and stability as compared with the other two catalysts with most of CuO located on the outer surface of the CaO–ZrO2 support, because the former has a higher specific surface area, enhanced synergistic effect and stronger interaction between the CaO–ZrO2 support and CuO active constituent.

Sulfur-Resistant CO Methanation to CH4 Over MoS2/ZrO2 Catalysts: Support Size Effect On Morphology and Performance of Mo Species

In this work, the effect of ZrO2 particle size on the surficial and structural properties and catalytic performance of Mo-based catalysts towards sulfur-resistant methanation was investigated. The results showed that the catalytic activity correlated closely with the particle size of ZrO2. The supports and catalysts were characterized by N2-adsorption, XRD, Raman, H2-TPR and TEM to obtain the information about their morphology and structure in order to understand the structure–activity relationship. The results evidence that smaller ZrO2 particle not only had higher surface area which was beneficial for the dispersion of surface Mo species, but also weaken the interaction between MoO3 and support. Since them, ZrO2 support with small particle size favors the formation of monolayer MoS2 with short length. Catalytic activity evaluation determined that MoS2/ZrO2 catalyst with smaller ZrO2 particle size exhibited higher catalytic activity of sulfur-resistant CO methanation due to more edge sites on MoS2.

Efficient conversion of furfural into cyclopentanone over high performing and stable Cu/ZrO2 catalysts

Currently, biomass transformation to produce high value-added chemicals and liquid biofuels is attracting more and more interest by the virtue of its importance in the sustainable development of human society. Herein, we reported the conversion of furfural (FFA) into cyclopentanone (CPO) in water over high performing and stable Cu/ZrO2 catalysts prepared by our developed one-pot reduction-oxidation method. It was demonstrated that surface structures and catalytic performances of catalysts could be delicately adjusted by varying the calcination temperatures for catalyst precursors. Especially, an appropriate calcination temperature of 500 °C could significantly enhance the interactions between surface Cu species and the ZrO2 support, thus greatly facilitating the formation of Cu+-O-Zr-like structure at the metal-support interface, and the resulting Cu/ZrO2 catalyst showed a superior catalytic performance with a high CPO yield of 91.3% under mild reaction conditions (i.e. a low hydrogen pressure of 1.5 MPa and 150 °C) to other metal oxides supported copper catalysts prepared by the conventional impregnation. It was revealed that in addition to surface acidic sites, surface Cu+/(Cu°+Cu+) ratio also played a key role in promoting the formation of CPO in the present Cu/ZrO2 catalytic system.

Efficient and stable Cu-Ni/ZrO2 catalysts for in situ hydrogenation and deoxygenation of oleic acid into heptadecane using methanol as a hydrogen donor

In this work, a series of ZrO2-supported Cu, Ni and bimetallic Cu-Ni catalysts were synthesized and evaluated for their activity and stability in the in situ hydrogenation and decarboxylation of oleic acid using methanol as a hydrogen donor. High-angle annular dark-field scanning transmission electron microscopy (HADDF-STEM), energy dispersive X-ray spectroscopy (EDS-mapping), X-ray diffraction (XRD) and temperature programmed reduction (TPR) characterizations revealed that the as-synthesized Cu-Ni/ZrO2 was a Cu-Ni alloy that was highly dispersed on mixed m-ZrO2 and t-ZrO2. The bimetallic Cu-Ni/ZrO2 nanostructures not only exhibited better catalytic activity for the conversion of oleic acid compared to monometallic Cu/ZrO2 and Ni/ZrO2 catalysts but also demonstrated good reuse performance. The formation of the Cu-Ni alloy facilitated the decarboxylation reaction and inhibited the cracking reaction, leading to enhanced catalytic performance. The good stability of Cu-Ni/ZrO2 was primarily due to the good hydrothermal stability of the ZrO2 support.

Influence mechanism of supports on the reactivity of Ni-based oxygen carriers for chemical looping reforming: A DFT study

First-principle calculations based on the density functional theory (DFT) were employed to clarify the influence mechanism of supports on the reactivity of Ni-based oxygen carriers for chemical looping reforming. We firstly built the models of two supported Ni-based oxygen carriers (NiO/ZrO2 and NiO/MgAl2O4 composites). It was found that NiO cluster is easy to attach to surface of two supports and the forming composites NiO/ZrO2 and NiO/MgAl2O4 are stable. Then surface reaction between CH4 and two supported NiO including the steps of CH4 sequential dehydrogenation (S1), H2 formation (S2) and CO formation (S3) was investigated. Compared with that for unsupported NiO, both supports addition significantly decreases the energy barrier of S1 process. For both supported NiO, the energy barriers increased in the order of S1 < S2 < S3, suggesting that the S3 process is the rate-limiting step in the surface reaction. The energy barrier (2.77 eV) of S3 process for NiO/ZrO2 is lower than that (3.07 eV) for NiO/MgAl2O4, implying that ZrO2 support is more conducive to the surface reaction. Moreover, our calculation results also found that the Ni4O4/ZrO2 OC has a lower the oxygen vacancy formation energy (Evac), which showed that the ZrO2 support makes Ni-O bond weaker than MgAl2O4 support. The C reacts more readily with the oxygen of NiO supported on ZrO2. The lower energy barrier of S3 process for ZrO2 support could be attributed to its higher activity of surface oxygen in the NiO. Therefore, it was concluded that NiO/ZrO2 oxygen carrier demonstrates relatively better reactivity. Our DFT calculations could provide a detailed understanding of the effect of supports on the reactivity of Ni-based oxygen carrier.

Ag-(Mo-W)/ZrO2 catalysts for the production of propylene oxide: Effect of pH in the preparation of ZrO2 support

Direct oxidation of propylene to propylene oxide was carried out over Ag-(Mo-W)/ZrO2 (pH X) catalysts prepared by changing the pH of Zr precursor solution from 3 to 14 while preparing the ZrO2 support. It was found that the fraction of monoclinic phase and the ratio of acidity to basicity in the catalysts showed a volcano-shaped trend with respect to pH of Zr precursor solution. Such characteristics were well correlated with the selectivity of reaction towards propylene oxide. Ag-(Mo-W)/ZrO2 (pH 10) with the highest fraction of monoclinic phase of ZrO2 and ratio of surface acidity to basicity showed the highest selectivity (68%) for propylene oxide.

Catalytic methane combustion over Pd/ZrO2 catalysts: Effects of crystalline structure and textural properties

Zirconia supports were synthesized via a precipitation method, and the effects of crystalline structure and textural properties of ZrO2 on the methane combustion reaction were investigated using the Pd/ZrO2 catalysts. Upon increasing the digestion temperature, the crystalline structure of ZrO2 was transformed from the mixed phase (monoclinic and tetragonal) to the pure tetragonal phase, and these tetragonal ZrO2 supported Pd catalysts exhibited good hydrothermal stabilities. In addition, the BET surface areas of the tetragonal ZrO2 supports could also be tuned by varying the digestion time and calcination temperature, and the catalysts supported on ZrO2 having lower BET surface areas exhibited enhanced catalytic activities. Therefore, the Pd/ZrO2(85) catalyst, which had a tetragonal structure in addition to the smallest BET surface area, gave the optimal catalytic performance. This is likely due to larger PdO particles being formed on this ZrO2(85) support, thereby resulting in a highly reducible PdO species. Finally, variations in reducibility between the monoclinic and the tetragonal supported catalysts were clearly calculated by the density functional theory.

In situ ATR-IR studies in aqueous phase reforming of hydroxyacetone on Pt/ZrO2 and Pt/AlO(OH) catalysts: The role of aldol condensation

In situ Attenuated Total Reflection Infrared (ATR-IR) spectroscopy was used to study Aqueous Phase Reforming of hydroxyacetone on Pt/AlO(OH) and Pt/ZrO2 catalysts at 230 °C/ 30 bar. Formation of strongly adsorbed aldol condensation products was observed on the surface of Pt/ZrO2 and ZrO2 in contrast to Pt/AlO(OH) and AlO(OH). Peak assignments were supported by DFT calculations of the IR spectra of the condensation products in vacuum and in the presence of water. Aldol condensation of hydroxyacetone leading to compounds with high molecular weight with unsaturated bonds was suggested as a first step in coke formation. Carbonaceous deposits on the surface of the ZrO2 support are oxygen-rich and highly reactive, according elemental analysis and TPO. Surprisingly, no adsorbed CO on Pt was observed in the spectra obtained under reaction conditions, suggesting that adsorbed CO is not involved in the rate-determining step in APR of hydroxyacetone.

Oxidative dehydrogenation and dry reforming of n-butane with CO2 over NiFe bimetallic catalysts

The oxidative dehydrogenation of n-butane to 1,3-butadiene using CO2 as a soft oxidant is investigated over oxide-supported NiFe bimetallic catalysts. Dry reforming of n-butane with CO2 to syngas is also studied under identical conditions for comparison. The Ni1Fe3/CeO2 catalyst is identified as a promising catalyst for the oxidative dehydrogenation to 1,3-butadiene via the CH bond cleavage, while the Ni3Fe1/CeO2 catalyst mainly promotes the dry reforming pathway via the CC bond scission. The oxidation states of Ni and Fe are determined by X-ray absorption fine structure (XAFS) measurements under reaction conditions. Density functional theory (DFT) calculations are performed to further understand the different reaction pathways. Furthermore, the effect of oxide supports is studied for the Ni1Fe3 bimetallic catalysts, showing that highly reducible supports, CeO2 and CeO2-ZrO2, promote the production of 1,3-butadiene, whereas the ZrO2 support significantly suppresses the oxidative dehydrogenation.