Hydrogen Production by Steam Reforming of Ethanol Over Mesoporous Ni–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> Catalysts

This review paper reports the recent progress concerning the application of nickel–alumina–zirconia based catalysts to the ethanol steam reforming for hydrogen production. Several series of mesoporous nickel–alumina–zirconia based catalysts were prepared by an epoxide-initiated sol–gel method. The first series comprised Ni–Al₂O₃–ZrO₂ xerogel catalysts with diverse Zr/Al molar ratios. Chemical species maintained a well-dispersed state, while catalyst acidity decreased with increasing Zr/Al molar ratio. An optimal amount of Zr (Zr/Al molar ratio of 0.2) was required to achieve the highest hydrogen yield. In the second series, Ni–Al₂O₃–ZrO₂ xerogel catalysts with different Ni content were examined. Reducibility and nickel surface area of the catalysts could be modulated by changing nickel content. Ni–Al₂O₃–ZrO₂ catalyst with 15 wt% of nickel content showed the highest nickel surface area and the best catalytic performance. In the catalysts where copper was introduced as an additive (Cu–Ni–Al₂O₃–ZrO₂), it was found that nickel dispersion, nickel surface area, and ethanol adsorption capacity were enhanced at an appropriate amount of copper introduction, leading to a promising catalytic activity. Ni–Sr–Al₂O₃–ZrO₂ catalysts prepared by changing drying method were tested as well. Textural properties of Ni–Sr–Al₂O₃–ZrO₂ aerogel catalyst produced from supercritical drying were enhanced when compared to those of xerogel catalyst produced from conventional drying. Nickel dispersion and nickel surface area were higher on Ni–Sr–Al₂O₃–ZrO₂ aerogel catalyst, which led to higher hydrogen yield and catalyst stability over Ni–Sr–Al₂O₃–ZrO₂ aerogel catalyst.     

Effect of Calcination Temperature on the Catalytic Oxidation of Formaldehyde Over Co<Subscript>3</Subscript>O<Subscript>4</Subscript>–CeO<Subscript>2</Subscript> Catalysts

The effect of calcination temperature (350–650?°C) on the structure and catalytic activity of Co₃O₄–CeO₂ mixed oxides prepared by sol–gel method was investigated by XRD, H₂-TPR, O₂-TPD and formaldehyde (HCHO) oxidation. The Co₃O₄–CeO₂ calcined at 450?°C (Co₃O₄–CeO₂-450) exhibited the best performance, showing that the complete oxidation of HCHO was achieved at temperature as low as 80?°C. The results of characterizations revealed that the Co₃O₄–CeO₂-450 had excellent catalytic activity due to the larger specific surface area, the best reducibility and more abundant surface active oxygen species.     

Hydrodeoxygenation of Vegetable Oil on NiMoS/WO<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts

Tungstate-containing aluminum oxide is suitable as a catalyst support for hydrodeoxygenation of sunflower oil, ensuring 81–83 wt % yield of liquid products at 380°С, 4.0 MPa, and feed space velocity of 1 h^–1. The catalyst acidity increases with increasing tungsten oxide content, leading to an increase in the content of decarboxylation/decarbonylation products and isoparaffins in the product mixture.     

Physicochemical properties of (CH<Subscript>3</Subscript>)<Subscript>2</Subscript>NH<Subscript>2</Subscript>Cl–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites

Composite solid electrolytes were synthesized from the organic salt dimethylammonium chloride (1–x)C₂H₈NCl–xAl₂O₃. Their physicochemical properties were studied. In the starting C₂H₈NCl salt, there is a phase transition at 39°C accompanied by an increase in conductivity by two orders of magnitude. The conductivity of the high-temperature phase is 9.3 × 10^–6 S/cm at 160°C. A differential scanning calorimetry study showed that the salt in the composites spreads over the oxide surface and at x > 0.6 the salt melting enthalpy decreases to zero. The conductivity of the resulting composites was studied by impedance spectroscopy. It was shown that heterogeneous doping leads to a sharp increase in ion conductivity to 7.0 × 10^–3 S/cm at 160°C and a decrease in the activation energy to 0.55 eV.     

Selective Hydrogenation of Acetylene and Physicochemical Properties of Pd–Fe/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Bimetallic Catalysts

The selective hydrogenation of acetylene on Pd–Fe/Al₂O₃ catalysts prepared by decomposition of ferrocene on reduced Pd/Al₂O₃ was studied. The effect of the conditions of treatment of the Pd–ferrocene/ Al₂O₃ precursor on the catalyst activity and selectivity was investigated, and the optimum conditions were determined at which the Pd–Fe/Al₂O₃ catalyst has higher selectivity than Pd/Al₂O₃ without any loss of activity.     

Hydrocracking of vacuum gas oil in the presence of catalysts NiMo/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–amorphous aluminosilicates and NiW/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–amorphous aluminosilicates

Supported nickel–molybdenum and nickel–tungsten hydrocracking catalysts prepared using a support that consists of 70% Al₂O₃ and 30% amorphous aluminosilicate were characterized by nitrogen and mercury porosimetry, IR spectroscopy of adsorbed CO, and high-resolution electron microscopy. The catalytic tests in hydrocracking of vacuum gas oil containing 3.39% sulfur showed that the nature of the hydrogenating component (NiMo or NiW) only slightly influences the vacuum gas oil conversion and the diesel fraction yield, but noticeable influences the properties of the diesel fraction obtained. The catalyst NiMo/Al₂O₃–amorphous aluminosilicates, compared to NiW/Al₂O₃–amorphous aluminosilicates, ensures lower sulfur content in the diesel fraction obtained, whereas the catalyst NiW/Al₂O₃–amorphous aluminosilicates allows obtaining a diesel fraction with lower content of polyaromatic compounds.     

Crystal structure of Cs[(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>2</Subscript>(OH)] · H<Subscript>2</Subscript>O

Single crystals of Cs[(UO₂)₂(C₂O₄)₂(OH)] · H₂O were synthesized and structurally studied using X-ray diffraction. The compound crystallizes in monoclinic space group P2₁/m, Z = 2, with the unit cell parameters a = 5.5032(4) Å, b = 13.5577(8) Å, c = 9.5859(8) Å, β = 97.012(3)°, V = 709.86(9) ų, R = 0.0444. The main building units of crystals are [(UO₂)₂(C₂O₄)₂(OH)]^? layers of the A₂K ₂ ⁰² M² (A = UO ₂ ²⁺ , K⁰² = C₂O ₄ ^2? , and M² = OH^?) crystal-chemical family. Uranium-containing layers are linked into a three-dimensional framework via electrostatic interactions with outer-sphere cations and hydrogen bonds with water molecules.     

Models of molecular structures of aluminum–iron clusters AlFe<Subscript>3</Subscript>, Al<Subscript>2</Subscript>Fe<Subscript>3</Subscript>, and Al<Subscript>2</Subscript>Fe<Subscript>4</Subscript> according to quantum-chemical DFT calculations

The geometrical parameters of molecular structures of three types of aluminum–iron clusters containing in total four, five, and six Al and Fe atoms in structural units have been calculated by the OPBE/TZVP density functional theory (DFT) method with the Gaussian09 program package. It has been found that the AlFe₃, Al₂Fe₃, and Al₂Fe₄ clusters can have four, eight, and nine structural modifications, which significantly differ in stability and geometric parameters. Bond lengths and bond and torsion (dihedral) angles are reported for each of these modifications.     

Effect of ZrO<Subscript>2</Subscript> on Catalyst Structure and Catalytic Sulfur-Resistant Methanation Performance of MoO<Subscript>3</Subscript>/ZrO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts

A series of MoO₃/ZrO₂–Al₂O₃ catalysts was prepared and investigated in the sulfur-resistant methanation aimed at production of synthetic natural gas. Different methods including impregnation, deposition precipitation, and co-precipitation were used for preparing ZrO₂–Al₂O₃ composite supports. These composite supports and their corresponding Mo-based catalysts were investigated in the sulfur-resistant methanation, and characterized by N₂ adsorption–desorption, XRD and H₂-TPR. The results indicated that adding ZrO₂ promoted MoO3dispersion and decreased the interaction between Mo species and support in the MoO₃/ZrO₂–Al₂O₃ catalysts. The co-precipitation method was favorable for obtaining smaller ZrO₂ particle size and improving textural properties of support, such as better MoO₃ dispersion and increased concentration of Mo⁶⁺ species in octahedral coordination to oxygen. It was found that the MoO₃/ZrO₂–Al₂O₃ catalyst with ZrO₂Al₂O₃ composite support prepared by co-precipitation method exhibited the best catalytic activity. The ZrO₂ content in the ZrO₂Al₂O₃ composite support was further optimized. The MoO₃/ZrO₂–Al₂O₃ with 15 wt % ZrO₂ loading exhibited the highest sulfur-resistant CO methanation activity, and excess ZrO₂ reduced the specific surface area and enhanced the interaction between Mo species and support. The N₂ adsorption-desorption results indicated that the presence of ZrO₂ in excessive amounts decreased the specific surface area since some amounts of ZrO₂ form aggregates on the surface of the support. The XRD and H₂-TPR results showed that with the increasing ZrO₂ content, ZrO₂ particle size increased. These led to the formation of coordinated tetrahedrally Mo⁶⁺(T) species and crystalline MoO₃, and this development was unfavorable for improving the sulfur-resistant methanation performance of MoO₃/ZrO₂–Al₂O₃ catalyst.     

Synthesis and properties of γ-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> solid solutions

The textural and structural properties of mixed oxides Ga₂O₃–Al₂O₃, obtained via impregnating γ-Al₂O₃ with a solution of Ga(NO₃)₃ and subsequent heat treatment, are studied. According to the results from X-ray powder diffraction, gallium ions are incorporated into the structure of aluminum oxide to form a solid solution of spinel-type γ-Ga₂O₃–Al₂O₃ up to a Ga₂O₃ content of 50 wt % of the total weight of the sample, accompanied by a reduction in the specific surface area, volume, and average pore diameter. It is concluded that when the Ga₂O₃ content exceeds 50 wt %, the β-Ga₂O₃ phase is observed along with γ-Ga₂O₃–Al₂O₃ solid solution. ⁷¹Ga and ²⁷Al NMR spectroscopy shows that gallium replaces aluminum atoms from the tetrahedral position to the octahedral coordination in the structure of γ-Ga₂O₃–Al₂O₃.     

Modifying additives affect the properties of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system

The effects caused by modifying additives, namely nonionic surfactants (Tween 80 and Neonol AF 9-6) and oxides (B₂O₃ and HfO₂), on the rheology, film formation, and phase formation in the yttrium aluminum silicate system prepared by sol–gel technology were studied. The effect of 1 wt % HfO₂ additions on the activation energy of crystallization was studied.     

Glass Formation in the Ternary System La<Subscript>2</Subscript>O<Subscript>3</Subscript>–As<Subscript>2</Subscript>S<Subscript>3</Subscript>–Er<Subscript>2</Subscript>O<Subscript>3</Subscript>

The boundaries of the glass formation region in the ternary system La₂O₃–As₂S₃–Er₂O₃ were found. Transparent glass of composition (La₂O₃)_0.03(As₂S₃)0.90(Er₂O₃)0.07 was studied by X-ray photoelectron and Raman spectroscopy. The intensities of the bands characterizing As–S, La–O, and Er–O bonds increased, and these bands were shifted toward higher energies. This was due to an increase in the covalence of these bonds and probably due to the formation of new bonds in the glasses. Samples in the glass formation region are resistant at 300 K to air, water, and organic solvents.     

P/RS intergrowth type phases in the Ln<Subscript>2</Subscript>O<Subscript>3</Subscript>–MO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> systems

Regularities of formation of complex aluminates with structure of P/RS intergrowth type phases in the Ln₂O₃–MO–Al₂O₃ systems (Ln = rare-earth element, M = Mg, Ca, Sr, Ba) have been considered. Systematization of the data on formation of complex compounds coexisting with one-layer phases in the Ln₂O₃–MO–Al₂O₃ systems and analysis of geometry criteria of LnMAlO₄ stability is a promising approach to prediction of novel compounds with structure of Ruddlesden–Popper phase.     

CeO<Subscript>2</Subscript>–ZrO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Modified by Selective Doping with SrO for Improved Pd-Only Three-Way Catalyst

Composite CeO₂–ZrO₂–Al₂O₃ (CZA) modified by selective doping with SrO was prepared by simple coprecipitation method. The characterization results reveal that the structural property of the modified sample is fundamentally different from that of undoped CZA, the doped SrO can selectively combine with Al₂O₃ and act as a stabilizer, meanwhile homogeneous CZ solid solution is formed which appears insusceptible to Al₂O₃. Consequently more lattice defects are created in CZAS, which facilitate the improvement of oxygen mobility. The UV–Vis DRS and XPS results demonstrate that after doping with SrO, the supported catalyst Pd/CZAS possesses higher surface Pd and Ce³⁺ concentrations, which consequently leads to improved reducibility and catalytic performance. Furthermore, the synergistic effect between CeO₂–ZrO₂ and SrO–Al₂O₃ helps improve the thermal stability of Pd/CZAS. As a result, after aging treatment, Pd/CZASa still maintains improved structural, textural, morphological and reduction properties along with enhanced three-way catalytic performance.     

Preparation and characterization of CeO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> aerogels supported ruthenium for catalytic wet air oxidation of p-hydroxybenzoic acid

Catalytic wet air oxidation of an aqueous solution of p-hydroxybenzoic acid was conducted over ruthenium catalysts (1 wt%) supported on CeO₂–Al₂O₃ aerogels mixed oxides at 140 °C and 50 bars of air. We study the effect of the amount of CeO₂ in the catalyst. We found that the optimal cerium content in the Al₂O₃ support was 20 wt%. The activity of the Ru/Al₂O₃ and Ru/CeO₂ was also tested for comparison. It was found that the addition of CeO₂ on the alumina support improves the activity of Ru catalysts. The activity of the samples decreases in the following order: Ru/Ce–Al (20) > Ru/Ce–Al (10) > Ru/Ce–Al (5) ≈ Ru/Al₂O₃ > Ru/CeO₂. Samples characterization was performed by means of N₂ adsorption–desorption, XRD, UV–Vis, TPR, SEM and TEM.     

Characterization of gold supported on Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–CuO–Mn<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts obtained by thermal decomposition of aerosols

The purpose of this work was to employ the differential thermal analysis (DTA) technique to compare variations in the collapse energy of the zeolite Y crystalline structure in a fresh catalyst and in the same catalyst impregnated with nickel and vanadium. A small exothermic signal in the DTA curve at 950–1150 °C indicated the collapse of the crystalline structure. The areas of the exothermic signals in the DTA curves of the two samples indicated a reduction in the curve of the metal impregnated catalyst. These results were compared with X-ray data, leading to the conclusion that metal impregnation affects the zeolite Y crystalline structure and that the DTA technique is a potentially useful tool for measuring the integrity of zeolite Y in catalysts.     

Pd/Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for the selective liquid-phase hydrogenation of acetylene to ethylene

The structure of Ga₂O₃–Al₂O₃ supports and Pd/Ga₂O₃–Al₂O₃ catalysts and the performance of these catalysts in liquid-phase acetylene hydrogenation have been investigated. The deposition of Ga(NO₃)₃ onto Al₂O₃ by impregnation followed by calcination of the impregnated support at 600°C yields γ-Ga₂O₃–Al₂O₃ solid solutions containing up to 50 wt % Ga₂O₃. X-ray diffraction characterization of model palladium catalysts and their temperature-programmed reduction with hydrogen have demonstrated that, while palladium in Pd/Ga₂O₃ is in the form of a Pd₂Ga alloy, in the Pd/γ-Ga₂O₃–Al₂O₃ catalyst there is no direct interaction between PdО and Ga₂O₃ particles and palladium is in the monometallic state. The introduction of 10–20 wt % gallium oxide into Al₂O₃ lowers the activity of the supported palladium catalyst relative to that of the initial Pd/Al₂O₃ but increases the ethylene yield by enhancing the ethylene formation selectivity.     

Glass Formation in the Al<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>3</Subscript>–(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>SO–H<Subscript>2</Subscript>O System

The glass formation in the Al₂(SO₄)₃–(CH₃)₂SO–H₂O system was found for the first time. The competitive ability of ligands, dimethyl sulfoxide and water (which are strong donors), for entering the first coordination sphere of aluminum is considered. The possibility of mixed coordination of (CH₃)₂SO (via sulfur and oxygen atoms) in the first coordination sphere of aluminum with retention of the glass-forming ability of the sample was suggested on the basis of IR spectral study.