Oxidative conversion of methane and methanol on M/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/cordierite structured metal oxide catalysts (m = Ni,Cu, Zn)

A study was carried out on the properties of Ni/Al₂O₃ and Cu-ZnO/Al₂O₃ composites supported on ceramic honeycomb monoliths made from synthetic cordierite in the carbon dioxide conversion of methane and the partial oxidation of methanol. The structured nickel-alumina catalysts are significantly more efficient than the conventional granulated catalysts. The improved working stability of these catalysts was achieved by adjusting the acid-base properties of the surface by introducing sodium and potassium oxides, which leads to inhibition of surface carbonization. The hydrogen yield was close to 90% in the partial oxidation of methanol with a stoichiometric reagent ratio in the presence of the Cu-ZnO/Al₂O₃/cordierite catalyst. A synergistic effect was found, reducing the selectivity of CO formation in the presence of the Cu-ZnO catalyst relative to samples derived from the individual components Cu and ZnO. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 5, pp. 299–306, September–October, 2007.     

The effect of spinel type support FeAlO<Subscript>3</Subscript>, ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript>, CrAl<Subscript>3</Subscript>O<Subscript>6</Subscript> on physicochemical properties of Cu,Ag, Au,Ru supported catalysts for methanol synthesis

The comparative study of the role of binary oxide support on catalyst physico-chemical properties and performance in methanol synthesis were undertaken and the spinel like type structures (ZnAl₂O₄, FeAlO₃, CrAl₃O₆) were prepared and used as the supports for 5% metal (Cu, Ag, Au, Ru) dispersed catalysts. The monometallic 5% Cu/support and bimetallic 1% Au (or 1% Ru)-5% Cu/support (Al₂O₃, ZnAl₂O₄, FeAlO₃, CrAl₃O₆) catalysts were investigated by BET, XRD and TPR methods. Activity tests in methanol synthesis of CO and CO₂ mixture hydrogenation were carried out. The order of Cu/support catalysts activity in methanol synthesis: CrAl₃O{ia6} > FeAlO₃ > ZnAl₂O₄ is conditioned by their reducibility in hydrogen at low temperature. Gold appeared more efficient than ruthenium in promotion of Cu/support catalysts. Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 2, pp. 242–248. The article is published in the original.     

Effect of the alkoxides addition order on the properties of Pd/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> catalysts used for methane combustion

A series of Pd/Al₂O₃–ZrO₂ catalysts were prepared to be used in methane oxidation. The effect of the addition order of metal alkoxides on the texture, structure and catalytic properties of the solids is studied. The control of the preparation parameters is achieved via sol gel way as an attractive route of the preparation of these catalysts. N₂ physisorption, XRD, Scanning Electronic Microscopy (SEM) and H₂ chemisorption are the main techniques used to characterize the prepared Pd/Al₂O₃–ZrO₂ catalysts. Textural analysis reveals the mesoporosity of all the catalysts independently of the addition order of alkoxides while surface area is more pronounced when the aluminium alkoxide is added before or with the zirconium precursor. XRD patterns show the development of the zirconia tetragonal phase for all the catalysts. Better metallic dispersion is obtained when aluminium alkoxide is added first which can be justified by the high homogeneity observed on the corresponding catalyst as revealed by SEM technique.     

Catalytic activity and physicochemical properties of Ni-Au/Al<Subscript>3</Subscript>CrO<Subscript>6</Subscript> system for partial oxidation of methane to synthesis gas

This work is focused on the role of gold and Al₃CrO₆ support for physicochemical properties, and catalytic activity of supported nickel catalysts in partial oxidation of methane (POM). Catalysts, containing 5% Ni and 5% Ni-2% Au active phases dispersed on mono- (Al₂O₃, Cr₂O₃) and bi-oxide Al₃CrO₆ support, were investigated by TPR, BET and XRD methods, and the activity tests in POM reaction were carried out. Bimetallic Ni-Au catalysts dispersed on Al₃CrO₆ support remained highly stable and active. The amorphous binary oxide Al₃CrO₆ can stabilize considerable amount of Cr⁴⁺, Cr⁵⁺, and Cr⁶⁺ species in Ni-Au/Al₃CrO₆ catalyst network during its calcination in the air. Nickel supported on binary oxide Ni/Al₃CrO₆ can form Ni(III)CrO₃ bi-oxide phase in reductive conditions. During TPR H2 reduction of Ni-Au/Al₃CrO₆ catalyst chromium(II) oxide Cr(II)O phase is observed. After POM reaction the existence of bimetallic Au-Ni alloy was experimentally confirmed on mono-oxide Al₂O₃ support surface, but its formation was not identified on bioxide Al₃CrO₆ support. Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 1, pp. 149–156. The article is published in the original. Based on a report at the VII Russ. Conf. on Mechanisms of Catalytic Reactions (with international participation), St. Petersburg, July 2–8, 2006.     

Synthesis,characterization, and catalytic activity in the <Emphasis Type="Italic">n</Emphasis>-heptane conversion over Pt/In–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> sol–gel prepared catalysts

Platinum catalysts supported on indium-doped alumina were prepared by the sol–gel method. The method allows the incorporation of In³⁺ in the alumina network. The indium-doped alumina supports showed narrow pore size distribution (5.4–4.0 nm) and high specific surface areas (258–280 m²/g). The ²⁷Al NMR-MAS spectroscopy identified aluminum in tetrahedral, pentahedral, and octahedral coordination; however, the intensity of the signal assigned to aluminum in pentahedral coordination diminishes with the increase of the content of indium. Total acidity determined by ammonia thermodesorption diminishes strongly in Pt/In–Al₂O₃ catalysts, suggesting a selective deposit of platinum over the acid sites of the support. The effect of the support in the platinum catalytic activity was evaluated in the n-heptane dehydrocyclization reaction. The selectivity patterns for such reaction were modified substantially in the doped Pt/In–Al₂O₃ catalysts, in comparison with the Pt-In/Al₂O₃–I coimpregnated reference catalyst. As an important result, the formation of benzene was suppressed totally over the indium-doped alumina sol–gel supports with a high content (3 wt%) of indium.     

An active phase transformation on surface of Ni-Au/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst during partial oxidation of methane to synthesis gas

It was studied the influence of gold addition on physico-chemical properties and catalytic activity of bimetallic Ni-Au/Al₂O₃ catalyst in partial oxidation of methane (POM). The reduction behavior in hydrogen, XRD crystal structure, XPS spectra and POM catalytic activity were investigated. The reduction of Ni-Au catalyst is a prerequisite condition to catalyze POM reaction. The formation of Ni-Au alloy during high temperature reduction in hydrogen and also in the conditions of POM reaction was experimentally proved. The addition of gold to Ni/Al₂O₃ system improves catalyst stability and activity in POM reaction.     

Influence of H<Subscript>2</Subscript>O and SO<Subscript>2</Subscript> on the activity of deposited cobalt oxide catalysts in the processes of reduction of nitrogen(I), (II) oxides with carbon monoxide and C<Subscript>3</Subscript>-C<Subscript>4</Subscript> alkanes

It is shown that palladium–cobalt oxide–cerium catalyst deposited on cordierite catalyzes the reduction of nitrogen(II) oxide with carbon monoxide, and cobalt–iron catalysts in simultaneous reduction of NO + N₂O with C₃-C₄ alkanes retained high activity in the presence of water vapor and sulfur dioxide. The Pd-Co₃O₄/cordierite catalyst exceeds the Pt-Co₃O₄/codierite catalyst in the conversion of NO and CO in the reaction mixture CO + NO + O₂ + H₂O + SO₂. Modification of the Pd-Co₃O₄/cordierite with cerium oxide considerably increases its sulfur resistance.     

Effect of the composition of the reaction atmosphere on the thermal stability of highly dispersed gold particles on an oxide support (Au/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system)

Metal gold particles were supported onto the surface of aluminum oxide by physical vapor deposition. The effects of thermal treatments at 30?800°C both in a vacuum and in an atmosphere of O₂ (5 mbar), CO (5 mbar), or a mixture of CO + O₂ (5 mbar of each) on the samples of Au/Al₂O₃ were studied by X-ray photoelectron spectroscopy. An increase in the Au4f line intensity in the course of gold deposition was accompanied by a shift of this line toward smaller binding energy. Upon the supporting of a maximum quantity of gold, the binding energy E _b(Au4f _7/2) became smaller than the value characteristic of the bulk metal. It was hypothesized that this can be explained by the formation of negatively charged Au^δ? particles due to electron density transfer from the support to the particles of gold. In the course of the heating of Au/Al₂O₃ in a vacuum or in a reaction atmosphere, the agglomeration of small gold particles occurred; this fact manifested itself in a decrease in the atomic ratio [Au]/[Al]. In all of the atmospheres, the Au particles supported on Al₂O₃ exhibited high thermal stability; considerable changes in the ratio [Au]/[Al] were observed only at temperatures higher than 600°C.     

Co-Mo/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Ni-W/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts: Potential and prospects for use in hydrotreating of light cycle oil from catalytic cracking

Со-Мо/Al₂O₃ and Ni-W/Al₂O₃ catalysts were tested in hydrotreating of light cycle oil from catalytic cracking, of the straight-run gasoil, and of their mixture under typical hydrotreating conditions used in industry. The catalysts prepared using PMo₁₂ and PW₁₂ heteropoly acids exhibit high catalytic activity. The Со-Мо/Al₂O₃ catalyst is more active in hydrodesulfurization and hydrogenation of olefin and diene hydrocarbons, whereas the Ni-W/Al₂O₃ catalysts are more active in hydrogenation of mono- and polycyclic aromatic hydrocarbons. Comparison of the quality characteristics of the hydrogenizates obtained with the requirements of the technical regulations shows that the required levels of the sulfur content and cetane number of the hydrogenizates at practically accessible process parameters can be reached for mixtures of the straight-run gasoil and light cycle oil from catalytic cracking with high content of the latter component only when the process with the Со-Мо/Al₂O₃ system and Ni-W/Al₂O₃ catalysts is performed in two steps.     

Investigation of macro-/mesoporous Re<Subscript>2</Subscript>O<Subscript>7</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts prepared by a particle-template method for butylene metathesis

Macro-/mesoporous Al₂O₃ supports were prepared by using monodisperse polystyrene (PS) microspheres as a template. The pore volume and BET surface area of the Al₂O₃ supports increased considerably with increasing amounts of the PS microspheres; further investigation showed that PS template only increased the volume of macro-pores but did not change the volume of meso-pores or micro-pores. Macro-/mesoporous Re₂O₇/Al₂O₃ metathesis catalysts were prepared through loading Re₂O₇ onto the as-prepared macro-/mesoporous Al₂O₃ supports, and their catalytic performance was tested in a fixed-bed tubular reactor using the metathesis of normal butylenes as a probe reaction. The results showed that the prepared macro-/mesoporous Re₂O₇/Al₂O₃ catalyst had high activity with consistent selectivity; propylene and pentene accounted for more than 90 wt% of the metathesis products, while the amount of ethylene plus hexane was less than 10 wt%, the majority of which was hexane. These Re₂O₇/Al₂O₃ catalysts had not only higher activity, but also longer working life span and higher tolerance to carbon residues than conventional Re₂O₇/Al₂O₃ catalysts.     

Role of rare-earth element oxides in catalysts for the oxidative conversion of methane based on Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

It has been established that oxides of the rare-earth elements with moderate redox potentials (La₂O₃, CeO₂) increased the activity and working stability of Ni-Al₂O₃/cordierite catalysts in the reactions of deep and partial oxidation of methane. In the presence of the (NiO + La₂O₃ + Al₂O₃)/cordierite catalyst the process of carbon dioxide conversion of methane can be intensified by introduction of oxygen into the reaction gas mixture which decreases the temperature to achieve high conversion to 75–100 °C and has practically no effect on selectivity with respect to H₂. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 6, pp. 359–364, November–December, 2008.     

Properties of the surface layer and catalytic activity of Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> with Pt or Pd additives in the oxidation of hydrogen

The catalytic activity in the oxidation of hydrogen (in the gaseous state in the presence of excess oxygen) has been studied for samples of Pt(Pd)/Ta₂O_5−x, formed by reduction with hydrogen. The samples obtained had greater activity than the traditional catalysts Pt(Pd)/Al₂O₃. According to X-ray diffraction analysis and electron microscopic studies, Ta₂O_5−x becomes amorphous with the formation of more reduced non-stoichiometric oxygen-deficient tantalum oxides with a surface layer of catalyst. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 3, pp. 180–185, May–June, 2008.     

Monolithic FeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for ammonia oxidation and nitrous oxide decomposition

(1.2–8.3)%FeO_х/Al₂O₃ monolith catalysts have been prepared by impregnating alumina with aqueous solutions of iron(III) nitrate and oxalate and have been tested in NH₃ oxidation and in the selective decomposition of N₂O in mixtures resulting from ammonia oxidation over a Pt–Rh gauze pack under conditions of nitric acid synthesis (800–900°C). In the case of the support calcined at 1200°C, the catalyst is dominated by bulk Fe₂O₃ particles localized on the Al₂O₃ surface. The activity of these samples in both reactions decreases with a decreasing active component content, thus limiting the potential of Fe₂(C₂O₄)₃ · 5H₂O, an environmentally friendlier but poorly soluble compound, as a substitute for Fe(NO₃)₃ · 9H₂O. Decreasing the support calcination temperature to 1000°C or below leads to the formation of a highly defective Fe–Al–O solid solution in the (1.2–2.7)%FeO_х/Al₂O₃ catalysts. The surface layers of the solid solution are enriched with iron ions or stabilize ultrafine FeO_х particles. The catalytic activity of these samples in both reactions is close to the activities measured for ~8%FeO_х/Al₂O₃ samples prepared using iron nitrate.     

The influence of hydrogen-containing molybdenum and tungsten bronzes on the catalytic activity of palladium composite catalysts for the oxidation of H<Subscript>2</Subscript>, CO,and CH<Subscript>4</Subscript>

The influence of hydrogen-containing molybdenum and tungsten bronzes on the catalytic activity of palladium composite catalysts for the oxidation of H₂, CO, and CH₄ was studied. It was found that the composite catalysts containing H _x MO₃ phases (M = W or Mo), which were formed by the reduction of MoO₃ and WO₃ oxides with hydrogen in the presence of deposited Pd, showed higher catalytic activity in the oxidation of small molecules (H₂, CO, and CH₄) with excess oxygen than the traditional Pd/Al₂O₃ deposited catalyst with the same content of the deposited metal. It was shown that the thermal stability of the H _x MO₃ phases was the limiting factor influencing the activity of these composite catalysts.     

Trimetallic NiMoW/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> hydrotreating catalyst based on H<Subscript>4</Subscript>SiMo<Subscript>3</Subscript>W<Subscript>9</Subscript>O<Subscript>40</Subscript> mixed heteropoly acid

Trimetallic NiMoW/Al₂O₃ catalyst was prepared using mixed H₄SiMo₃W₉O₄₀ heteropoly acid of Keggin structure and nickel citrate. Bimetallic NiMo/Al₂O₃ and NiW/Al₂O₃ catalysts based on H₄SiMo₁₂O₄₀ and H₄SiW₁₂O₄₀, respectively, were synthesized as reference samples. The use of mixed H₄SiMo₃W₉O₄₀ heteropoly acid as an oxide precursor allows the tungsten sulfidation degree and the degree of promotion of active phase particles to be increased. The hydrodesulfurization activity is enhanced as compared to NiW/Al₂O₃ catalyst. The synergistic enhancement of the activity of the NiMo₃W₉/Al₂O₃ catalyst relative to the bimetallic analogs is probably caused by formation of new mixed promoted active sites for direct desulfurization.     

Studies on the synthesis of higher alcohol over modified Cu/ZnO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

Higher alcohol has been considered as a potential fuel additive. Higher alcohol, including C₂–C₄ alcohol was synthesized by catalytic conversion of syngas (with a ratio of CO/H₂?=?1) derived from natural gas over modified Cu/ZnO/Al₂O₃ catalyst. Modified Cu/ZnO/Al₂O₃ catalysts promoted by alkali metal (Li) for higher alcohol synthesis (HAS) were prepared at different pH (6, 6.5, 7, 8, and 9) by co-precipitation to control Cu surface area and characterized by N₂ physisorption, XRD, SEM, H₂-TPR and TPD. The HAS reaction was carried out under a pressure of 45 bar, GHSV of 4000 h^?1, ratio of H₂/CO?=?1, and temperature ranges of 240 and 280 °C. It was found that the malachite phase of copper causes the size of copper to be small, which is suitable for methanol synthesis. Methanol and HAS share a common catalytic active site and intermediate. It was also found that the productivity to higher alcohol was correlated with Cu surface area.     

Selective oxidation of carbon monoxide in hydrogen-containing gas on CuO-CeO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts prepared by surface self-propagating thermal synthesis

The CuO-CeO₂/Al₂O₃ catalysts for the selective oxidation of CO in hydrogen-containing mixtures were prepared by surface self-propagating thermal synthesis (SSTS) with the use of cerium nitrate Ce(NO₃)₃, the ammonia complex of copper acetate [Cu(NH₃)₄](CH₃COO)₂, and citric acid C₆H₈O₇ as a fuel additive. The effect of the C₆H₈O₇/Ce(NO₃)₃ molar ratio on the catalyst activity and selectivity for oxygen was studied. The catalyst samples were studied by X-ray diffraction (XRD) analysis, temperature-programmed reduction (TPR-H₂), IR spectroscopy of adsorbed CO, and transmission electron microscopy (TEM). It was found that an increase in the C₆H₈O₇/Ce(NO₃)₃ ratio resulted in an increase in the degree of dispersion of the resulting CeO₂ phase. The greatest amount of dispersed CuO particles, which are responsible for catalytic activity in the oxidation of CO, was formed at C₆H₈O₇/Ce(NO₃)₃ = 1.     

Structure and Catalytic Properties of Ceria-based Nickel Catalysts for CO<Subscript>2</Subscript> Reforming of Methane

Carbon dioxide reforming (CDR) of methane to synthesis gas over supported nickel catalysts has been reviewed. The present review mainly focuses on the advantage of ceria based nickel catalysts for the CDR of methane. Nickel catalysts supported on ceria–zirconia showed the highest activity for CDR than nickel supported on other oxides such as zirconia, ceria and alumina. The addition of zirconia to ceria enhances the catalytic activity as well as the catalyst stability. The catalytic performance also depends on the crystal structure of Ni–Ce–ZrO₂. For example, nickel catalysts co-precipitated with Ce_0.8Zr_0.2O₂ having cubic phase gave synthesis gas with CH₄ conversion more than 97% at 800 °C and the activity was maintained for 100 h during the reaction. On the contrary, Ni–Ce–ZrO₂ having tetragonal phase (Ce_0.8Zr_0.2O₂) or mixed oxide phase (Ce_0.5Zr_0.5O₂) deactivated during the reaction due to carbon formation. The enhanced catalytic performance of co-precipitated catalyst is attributed to a combination effect of nano-crystalline nature of cubic Ce_0.8Zr_0.2O₂ support and the finely dispersed nano size NiO _x crystallites, resulting in the intimate contact between Ni and Ce_0.8Zr_0.2O₂ particles. The Ni/Ce–ZrO₂/θ–Al₂O₃ also exhibited high catalytic activity during CDR with a synthesis gas conversion more than 97% at 800 °C without significant deactivation for more than 40 h. The high stability of the catalyst is mainly ascribed to the beneficial pre-coating of Ce–ZrO₂ resulting in the existence of stable NiO _x species, a strong interaction between Ni and the support, and an abundance of mobile oxygen species in itself. TPR results further confirmed that NiO _x formation was more favorable than NiO or NiAl₂O₄ formation and further results suggested the existence of strong metal-support interaction (SMSI) between Ni and the support. Some of the important factors to optimize the CDR of methane such as reaction temperature, space velocity, feed CO₂/CH₄ ratio and H₂O and/or O₂ addition were also examined.     

Catalytic properties of Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts in the aqueous-phase reforming of ethylene glycol: Effect of the alumina support

The influence of the alumina support on the catalytic activity of Pt/Al₂O₃ catalysts in aqueous phase reforming of ethylene glycol to hydrogen was studied. The catalysts were prepared by impregnation of γ-, δ-, and α-alumina with H₂PtCl₆. The highest rate of hydrogen production (452 μmol min⁻¹ g⁻¹) obtained with the Pt/α-Al₂O₃ catalyst can be related to the highest extent of dispersion of Pt on α-Al₂O₃. XPS, TEM-EDX and TPR-H₂ measurements showed the absence of chloride-containing surface complexes in the Pt/α-Al₂O₃ catalyst. However, chloride-containing entities were found on the surface of Pt/γ-Al₂O₃ and Pr/δ-Al₂O₃ catalysts. When chloride ions are removed chlorinated Pt species facilitate the sintering of Pt crystallites and in this way affect the extent of Pt dispersion. Moreover, depending upon the particular crystalline form, alumina atoms have different coordination and alumina surfaces contain varying amounts of OH groups of different nature which affect the interaction between Pt and the support.     

Sub-nanometer-thick Al2O3 Overcoat Remarkably Enhancing Thermal Stability of Supported Gold Catalysts

Supported gold nanoparticle catalysts show extraordinarily high activity in many reactions. While the relative poor thermal stability of Au nanoparticles against sintering at elevated temperatures severely limits their practical applications. Here atomic layer deposition (ALD) of TiO₂ and Al₂O₃ was performed to deposit an Au/TiO₂ catalyst with precise thickness con-trol, and the thermal stability was investigated. We surprisingly found that sub-nanometer-thick Al₂O₃ overcoat can su ciently inhibit the aggregation of Au particles up to 600 C in oxygen. On the other hand, the enhancement of Au nanoparticle stability by TiO₂ overcoat is very limited. Di use reffectance infrared Fourier transform spectroscopy (DRIFTS) of CO chemisorption and X-ray photoelectron spectroscopy measurements both con rmed the ALD overcoat on Au particles surface and suggested that the presence of TiO₂ and Al₂O₃ ALD overcoat on Au nanoparticles does not considerably change the electronic properties of Au nanoparticles. The catalytic activities of the Al₂O₃ overcoated Au/TiO₂ catalysts in CO oxidation increased as increasing calcination temperature, which suggests that the embed-ded Au nanoparticles become more accessible for catalytic function after high temperature treatment, consistent with our DRIFTS CO chemisorption results.