Preparation,characterization and hydrotreating performances of ZrO2–Al2O3-supported NiMo catalysts

A series of Al₂O₃–ZrO₂ composite supported NiMo catalysts with various ZrO₂ contents were prepared. Several techniques including XRD, SEM, N₂ physisorption, H₂-TPR, and UV–vis DRS were used for typical physico-chemical properties characterization of the ZrO₂–Al₂O₃ composite supports and their NiMo/ZrO₂–Al₂O₃ catalysts. The test results showed that the composite supports prepared by the chemical precipitation method existed as amorphous phase in the samples with insufficient contents of ZrO₂, and the incorporation of ZrO₂ into supports provided a better dispersion of NiMo species, which made their reductions become easier. The pyridine-adsorbed FT-IR results indicated that the Lewis acid sites of catalysts increased significantly by the introduction of ZrO₂ into the supports. The activities of these catalysts for diesel oil hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) were evaluated in a high pressure micro-reactor system. The results showed that the ZrO₂–Al₂O₃-supported NiMo catalysts with suitable ZrO₂ contents exhibited much higher catalytic activities than that of Al₂O₃-supported one, and when the ZrO₂ contents were 15% and 5%, the NiMo/Al₂O₃–ZrO₂ catalysts presented the highest HDS and HDN activities, respectively.     

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

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

Influences of particle size and crystallinity of highly loaded CuO/ZrO2 on CO2 hydrogenation to methanol

In this study, highly loaded CuO (65.2 wt%) on ZrO₂ support was prepared by flame spray pyrolysis, and the effects of their particle sizes and ZrO₂ crystallinity on CO₂ hydrogenation to methanol were investigated. By varying the precursor feed rate (1–10 mL min⁻¹), the crystallite size (3–7 nm) and the crystallinity of tetragonal ZrO₂ were controlled. After H₂ reduction at 300°C, the Cu species in the catalysts, prepared at the feed rate = 2–10 mL min⁻¹, were converted to Cu particles (approximately 10–20 nm); however, the size and crystallinity of ZrO₂ remained the same. The activity and selectivity of the catalysts prepared at the feed rate = 2–3 mL min⁻¹ were higher than those of the catalysts prepared at the feed rates = 5–10 mL min⁻¹, because the smaller ZrO₂ particles in the former provided more surface to stabilize small Cu particles and from interfacial Cu-ZrO₂ sites (active sites).     

Photocatalytic water splitting over ZrO2 prepared by precipitation method

ZrO₂ prepared by the precipitation method of zirconium oxychloride with various hydrolyzing agents was studied for photocatalytic water splitting reaction under UV light irradiation. The crystal structure as well surface properties were varied with the hydrolyzing agent of KOH, NH₄OH, and NH₂CONH₂. Especially, the surface area of the prepared ZrO₂ calcined at the same temperature of 750 °C for 6 h was dependent highly on the hydrolyzing agent, and thus the highest photocatalytic activity was obtained for ZrO₂ with the highest surface area when KOH was used as a hydrolyzing agent, In the presence of Na₂CO₃, the photocatalytic activity of ZrO₂ increased by 2–3 fold, which was ascribed to the physically adsorbed carbonate species on the ZrO₂ surface. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Characterization and Catalytic Behavior of Potassium-Modified ZrO2 Base Catalysts

Potassium-modified ZrO₂ base catalysts were prepared by wet impregnation of hydrous zirconia and anhydrous zirconia with potassium compounds and calcined at 600 °C in air. The properties of the catalysts were characterized and compared. Catalytic activities were examined for the vapor-phase double-bond isomerization of 1-butene at 150 °C and the liquid-phase Michael addition of 2-methylcyclohexane-1,3-dione to methyl vinyl ketone at room temperature. The properties of the modified ZrO₂ i.e., basic site strength, were greatly affected by the ZrO₂ precursors and the potassium modifiers. High yields of 2-butene with relatively high cis/trans ratios were found. Leaching of the potassium-modified ZrO₂ makes the system less suitable for use in liquid-phase reactions.     

Combustion of a trace amount of CH4 in the presence of water vapor over ZrO2-supported Pd catalysts

Combustion of a trace amount of CH₄ over Pd catalysts supported on calcined ZrO₂ was examined under nearly exhaust gas conditions where the temperature is not so high and water vapor coexists. High catalytic activity was obtained with ZrO₂ support calcined at 1073 and 1273 K. The durability test at 673 K for 100 h revealed that the activity of these catalysts hardly decreased, while that of the Pd catalysts supported on calcined Al₂O₃ were much decreased in the course of time. These results demonstrated the advantages of ZrO₂ as a support for Pd catalysts in the present reaction. This revised version was published online in November 2006 with corrections to the Cover Date.     

Characterization of Supported NiSO4 and Effect of TiO2–ZrO2 Composition on Catalytic Activity for Acid Catalysis

A series of catalysts, NiSO₄/TiO₂–ZrO₂ having different TiO₂–ZrO₂ composition, for acid catalysis was prepared by the impregnation method using an aqueous solution of nickel sulfate. The addition of TiO₂ to ZrO₂ improved the surface area of the catalyst and enhanced its acidity remarkably because of the formation of new acid sites through the charge imbalance of Ti–O–Zr bonding. The binary oxide, TiO₂–ZrO₂ calcined above 600 °C resulted in the formation of crystalline orthorhombic phase of ZrTiO₄. Therefore, NiSO₄/TiO₂–ZrO₂ calcined at 500 °C exhibited a maximum catalytic activity for acid catalysis, and then the catalytic activity decreased with the calcination temperature. The correlation between catalytic activity and acidity held for both reaction, 2-propanol dehydration and cumene dealkylation. NiSO₄ supported on 50TiO₂–50ZrO₂ (TiO₂/ZrO₂ ratio = 1) among TiO₂–ZrO₂ binary oxides exhibited the highest catalytic activity for acid catalysis.     

Reduction of NO by CO on Cu/ZrO2/Al2O3 catalysts: Characterization and catalytic activities

ZrO₂, γ-Al₂O₃ and ZrO₂/γ-Al₂O₃-supported copper catalysts have been prepared, each with three different copper loads (1, 2 and 5 wt%), by the impregnation method. The catalysts were characterized by nitrogen adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR) with H₂, Raman spectroscopy and electronic paramagnetic resonance (EPR). The reduction of NO by CO was studied in a fixed-bed reactor packed with these catalysts and fed with a mixture of 1% CO and 1% NO in helium. The catalyst with 5 wt% copper supported on the ZrO₂/γ-Al₂O₃ matrix achieved 80% reduction of NO. Approximately the same rate of conversion was obtained on the catalyst with 2 wt% copper on ZrO₂. Characterization of these catalysts indicated that the active copper species for the reduction of NO are those in direct contact with the oxygen vacancies found in ZrO₂.     

Selective acetylation of glycerol over CeO2–M and SO42−/CeO2–M (M = ZrO2 and Al2O3) catalysts for synthesis of bioadditives

The feasibility of acetylation of glycerol with acetic acid was investigated employing CeO₂–ZrO₂, CeO₂–Al₂O₃, SO₄^2?/CeO₂–ZrO₂, and SO₄^2?/CeO₂–Al₂O₃ solid acid catalysts to synthesize monoacetin, diacetin and triacetin having interesting applications as bioadditives for petroleum fuels. Intensive physicochemical and surface characterization of the prepared catalysts were performed using XRD, BET surface area, ammonia-TPD and Raman spectroscopy techniques. Characterization results revealed that impregnated sulfate ions strongly influence the physicochemical characteristics of the investigated mixed oxide catalysts. Among various catalysts investigated, the SO₄^2?/CeO₂–ZrO₂ combination catalyst exhibited superior catalytic activity under mild conditions. The effect of various parameters such as reaction temperature, molar ratio of acetic acid to glycerol, catalyst wt% and time-on-stream were studied over the SO₄^2?/CeO₂–ZrO₂ catalyst to optimize the reaction conditions. Catalyst reusability was also carried out to understand its stability.     

Catalytic activities and properties of mesoporous sulfated Al2O3–ZrO2

Mesoporous sulfated Al₂O₃–ZrO₂ (MSAZ) catalysts with large surface areas and pore volumes after calcination at high temperature (650 °C) and with higher Al₂O₃ content than 20wt% were successfully prepared from a template of block copolymer (P84). The MSAZ catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption, transmission electron microscopy (TEM), ²⁷Al magic-angle spinning nuclear magnetic resonance (MAS NMR), thermogravimetric analysis (TG–DTG), temperature-programmed desorption of ammonia (NH₃-TPD) and infrared spectra (IR) of adsorbed pyridine. It is shown that the resulting mesostructured sulfated Al₂O₃–ZrO₂ samples have a well-developed textural mesoporosity. The number of acid sites present on MSAZ catalysts is higher than that on conventional sulfated zirconia, and the former catalysts are more active than the latter one for various acid-catalyzed reactions.     

Catalytic hydrolysis of chlorofluorocarbon (CFC-12) over WO3/ZrO2

The catalytic decomposition of CFC-12 (CCl₂F₂) in the presence of water vapor was investigated over a series of solid acids WO₃/ZrO₂. Compared with tungstic acid, ammonium metatungstate is a better source of tungsten oxide for the preparation of WO₃/ZrO₂ catalysts. CFC-12 decomposition activities of WO₃/ZrO₂ catalysts are in good agreement with their acidities. Enhancing the acidities of catalysts is favorable to increase their CFC-12 decomposition activities. WO₃/ZrO₂ catalysts calcined at higher temperature exhibit good catalytic activity and stability for the hydrolysis of CFC-12, and show better structural stability during the reaction.     

Surface phase transformation of ZrO2 in VOx/ZrO2 catalysts for boosting propane nonoxidative dehydrogenation

The nanocatalysts of VO_x deposited on ZrO₂ supports with single monoclinic (ZrO₂-M), tetragonal (ZrO₂-T), and binary monoclinic-tetragonal (ZrO₂-MT) phase were synthesized. VO_x/ZrO₂-MT catalysts exhibit better performance during propane nonoxidative dehydrogenation than VO_x/ZrO₂-M and VO_x/ZrO₂-T catalysts. Among VO_x/ZrO₂-MT catalysts, the conversion and deactivation rate constant of VO_x/ZrO₂-M₃₁T₆₉ catalyst is 35.2% and 0.22 h⁻¹, respectively. The promoting role of ZrO₂-MT is revealed by experiments and theoretical calculations. The MT-mixed phase structure in VO_x/ZrO₂-MT catalyst improves the structural properties and dispersion of VO_x. The tetragonal-monoclinic transformation on the ZrO₂-MT surface facilitates VO_x reduction and produces additional V³⁺ active sites. The highly dispersed V³⁺ sites on the ZrO₂-MT surface accelerate C H bond breaking and boost the desorption of propylene, which is the key reason for enhancing activity and stability during the reaction, respectively. Insight into the role of surface phase transformation of ZrO₂-MT is expected to obtain high-efficient catalysts further.     

The structure and surface acidity of zirconia-supported tungsten oxides

The structure and surface acidity of zirconia-supported tungsten oxide are studied by using BET, XRD, FT Raman, Tian–Calvet microcalorimetry as well as XPS. Three different crystal forms of ZrO₂ and their hydroxide precursors were prepared in a controllable way. It was found that the starting material and preparing conditions used have a significant effect on the structure of ZrO₂ obtained. The tungstate species on zirconium hydroxide generally promote the transformation of the hydroxide precursor into tetragonal ZrO₂, while the same species on the pre-calcined ZrO₂ has less effect during calcination. A bulk-phase WO₃ existed in the samples prepared by initially impregnating the monoclinic, tetragonal and cubic ZrO₂ or the hydroxide precursors of m- and t-ZrO₂, while no crystalline WO₃ was present in the samples prepared by initially impregnating the hydroxide precursor of c-ZrO₂. Raman results revealed that the surface tungstate(s) on three different zirconium hydroxides or their respective zirconia have similar structural features before calcination. The surface tungsten oxides and some WO₃ bulk phase are the detectable tungsten species in the final samples, the ratio of each component is strongly dependent on the preparation history and the nature of the support. Creation of very strong acidic sites on the zirconia-supported tungsten oxide is related to the crystal form of zirconia itself, the type of tungsten oxide species, and the cooperation between the surface tungsten oxide overlayer and zirconia. The strong acidic sites can be completely poisoned by the remaining sodium ion impurities, but have not been appreciably influenced by added yttrium component. The crystalline WO₃ seems of little importance in building up the strong surface acidity. This revised version was published online in July 2006 with corrections to the Cover Date.     

WGS activity of a novel Cu–ZrO2 catalyst prepared by a reflux method. Comparison with a conventional impregnation method

The activity in the WGS reaction of Cu/ZrO₂ catalysts prepared by a method of refluxing in an aqueous NH₄OH solution is studied. It is shown that at 3% Cu load the methods of impregnation over monoclinic or tetragonal ZrO₂ do not produce active catalysts for the WGS reaction. However, the method of refluxing generates highly active catalysts with Cu loads of 3% (w/w) or higher. The activity of the catalysts prepared by refluxing is associated with the formation of small Cu clusters, which would allow the regrouping of the H atoms to generate molecular H₂ in the presence of the crystalline tetragonal ZrO₂.     

Electron Paramagnetic Resonance investigation of the nature of active species involved in carbon black oxidation on ZrO2 and Cu/ZrO2 catalysts

To identify the nature of active paramagnetic species involved in the carbon black (CB) oxidation, an Electron Paramagnetic Resonance (EPR) study of (CB–ZrO₂) and (CB–Cu/ZrO₂) loose contact mixtures treated under argon flow has been undertaken. In the presence of pure zirconia catalysts, it was found that ZrO₂ interacts with CB and can be reduced into Zr³⁺ formed in tetragonal phase of this oxide support. In parallel, several EPR signals assigned to carbonaceous radicals were detected: i) carbonaceous radicals on CB surface, ii) radicals located at the CB–ZrO₂ interface and iii) oxygen deficit carbonaceous radicals observed at high treatment temperature. The carbonaceous signals disappeared completely after CB oxidation in agreement with a regeneration of the catalyst treated under air.For copper supported on zirconia catalysts, oxygen surrounding isolated Cu(II) species and oxygen from tetragonal ZrO₂ lattice are involved in carbon black oxidation. The phenomenon is reversible and this catalyst is also regenerated by air. Carbonaceous radical signals were also observed for (CB–Cu/ZrO₂) mixture and their intensity decrease versus temperature appeared in good agreement with the better activity of Cu/ZrO₂ compared to pure ZrO₂.     

Preparation of Co3O4/ZrO2(Y2O3) Catalyst and its Enhanced Catalytic Oxidation of CO

Yttria-stabilized zirconia powders were prepared by the sol–gel method coupled with supercritical CO₂ fluid-drying technology, using ZrOCl₂·8H₂O as the precursor, urea as the precipitant, and yttria as the stabilizer. The particles were characterized by X-ray diffraction, TEM and BET. The Co₃O₄/ZrO₂(Y₂O₃) catalysts were prepared by the impregnation method. The content of cobalt was varied from 5 to 12 wt%. The prepared catalysts were calcined at 200–500 °C and the pretreating temperature was varied from 200–400 °C. The performance of CO catalytic oxidation was tested and the catalyst with 8% Co loading, calcined at 200 °C, and with a pretreating temperature of 300 °C, showed the highest catalytic activity. The temperature for 95% CO conversion was as low as 113 °C; and, the catalyst showed both good cycling stability and excellent long-term stability.     

The influence of preparation method on the properties of NiMo sulfide catalysts supported on ZrO2

Highly loaded supported (Ni)Mo sulfide catalysts prepared using different methods have been studied. Two zirconia supports of high specific surface area were used, including amorphous or tetragonal ZrO₂ solids. The order of active components introduction as well as thermal treatment conditions were varied. The best performance in the reactions of hydrodesulfurisation of thiophene and hydrogenation of tetralin was shown by the coimpregnated systems sulfidized without calcination of the oxide precursor. Crystallized ZrO₂ support always provides higher activities in both reactions, than amorphous zirconia, despite very high specific surface area of the last. The differences between variously treated systems were explained using the results of characterizations including laser Raman spectroscopy, XPS spectroscopy and temperature programmed reduction.     

Influences of preparation methods of ZrO2 support and treatment conditions of Cu/ZrO2 catalysts on synthesis of methanol via CO hydrogenation

ZrO₂ supports were prepared by different methods (conventional precipitation method, shortened as “CP”, and alcogel/thermal treated with nitrogen method, shortened as “AN”), and Cu/ZrO₂ catalysts were prepared by impregnation method. The supports and catalysts were characterized by BET, XRD, TEM and TPR. The effects of the preparation methods of ZrO₂ supports and the treatment conditions (calcination and reduction temperatures) of the catalyst precursors on the texture structures of the supports and catalysts as well as on the catalytic performances of Cu/ZrO₂ in CO hydrogenation were investigated. The results showed that the support ZrO₂-AN had larger BET specific surface area, cumulative pore volume and average pore size than the support ZrO₂-CP. Cu/ZrO₂-AN catalysts showed higher CO hydrogenation activity and selectivity of oxygenates (C₁–C₄ alcohols and dimethyl ether) than Cu/ZrO₂-CP catalysts. Calcination and reduction temperatures of supports and catalyst precursors affected the catalytic performance of Cu/ZrO₂. The conversion of CO and the STY of oxygenates were 12.7% and 229 g/kg h, respectively, over Cu/ZrO₂-AN-550 at the conditions of 300 °C, 6 MPa.     

Low temperature complete combustion of dilute toluene and methyl ethyl ketone over Mn‐doped ZrO2 (cubic) catalysts

Combustion of dilute toluene and methyl ethyl ketone over Mn‐doped ZrO₂ catalysts prepared using different precipitating agents, such as tetra‐alkyl ammonium hydroxides and NH₄OH, having Mn/Zr ratios from 0.05 to 0.67, and calcined at different temperatures has been thoroughly investigated. The Mn‐doped ZrO₂ catalyst shows high toluene or methyl ethyl ketone combustion activity, particularly when its ZrO₂ is in cubic form, when its Mn/Zr ratio is close to 0.2, and when it is prepared using tetra‐methyl ammonium hydroxide as a precipitating agent and calcined at 773 K. Copyright © 2005 Society of Chemical Industry     

Isobutane oxydehydrogenation on SiO2-supported nickel molybdate catalysts: Effect of the active phase loading

The oxidative dehydrogenation of isobutane over SiO₂-supported and unsupported NiMoO₄ was studied under steady state conditions and the effect of active phase loading analysed.The SiO₂-supported catalysts were prepared by direct precipitation of NiMoO₄ on the support and characterised by BET, X-ray diffraction and temperature-programmed desorption of NH₃. Used catalysts were characterised by thermal analysis. Results show that, in SiO₂-supported catalysts, β-NiMoO₄ is stabilised even at room temperature. The SiO₂-supported NiMoO₄ catalyst with lower contents of active phase (13% NiMoO₄/SiO₂ and 26% NiMoO₄/SiO₂) present higher amount of β phase and less acidic surfaces.Besides isobutene, the reaction of isobutane over the prepared catalysts leads to the formation of CO₂, CO, light alkanes and coke. Unsupported NiMoO₄ leads to much higher amounts of total oxidation products and coke than the supported catalysts. The catalyst containing the highest amounts of β-phase (26% NiMoO₄/SiO₂) leads to higher selectivity to isobutene.