Effect of Mechanochemical Activation on the Catalytic Properties of Ferrites with the Spinel Structure

It was found experimentally that stacking defects formed in the mechanochemical activation of zinc ferrite enhanced the specific catalytic activity in the reaction of CO oxidation. The specific rate of CO oxidation was a linear function of defect concentration, which was determined using Mössbauer spectroscopy and X-ray diffraction. A conclusion was drawn that the same centers are responsible for an increase in the catalytic activity, the sorption capacity for hydrogen sulfide, and the reactivity of zinc ferrite in the interaction with hydrochloric acid. It was assumed that analogous factors caused an increase in the catalytic activity and reactivity of magnesium ferrite.     

Controlling the Catalytic Properties of Copper-Containing Oxide Catalysts

The results of a systematic study of the formation of Cu–Zn, Cu–Zn–Al, Cu–Zn–Cr, Cu–Zn–Si, Cu–Cr, and Cu–Si oxide catalysts with a widely varied ratio between their components are generalized within the chemical approach developed by G.K. Boreskov to establish the quantitative relation between their chemical composition and catalytic activity. Simultaneously, their catalytic properties, such as selectivity and activity, are measured under the same conditions in the methanol synthesis and dehydrogenation and water gas shift reactions, whose common feature is a reductive reaction medium. The activity of Cu–Zn–Al–Cr— Si-oxide catalysts in all the studied reactions is governed by the Cu⁰ nanoparticles formed on their surface in the process of reductive activation. Nanoparticles of different catalysts have similar sizes (3–8 nm). However, the ratios between the catalytic activities per unit of the copper surface area for catalysts with various structures of their oxide support (spinel, wurtzite, zincsilite, or silica type) are appreciably different in each reaction. The relation between the chemical composition of a catalyst and its catalytic activity in a certain reaction is established by the chemical composition of its precursor representing a hydroxo compound, i.e., the nature of the selected cations and the quantitative ratio between them. The decomposition of hydroxo compounds to oxides (and the further activation of oxides) should be performed at medium temperatures, providing the incomplete elimination of ОН^– and CO₃^2- anions, i.e., the formation of anion-modified oxides. The structure of the latter and the type of interaction between Cu⁰ nanoparticles and an oxide support are governed by the structure of the hydroxo precursor compound.     

Effect of the Sulfate Sulfur Content and the Preparation Procedure on the Catalytic Properties of Sulfated Zirconium Oxide

The effects of the composition and the procedure of preparing sulfated zirconium oxides on their catalytic properties in the reactions of 1-butene isomerization to 2-butenes and isobutanol dehydration were studied. The activity was found to depend on the nature of parent zirconium oxide, the sulfate sulfur content, and the temperature of calcination. Catalysts prepared from a crystalline oxide exhibited the highest activity. Their activity depends on the sulfate sulfur content. The calcination of catalysts at temperatures higher than 400°C resulted in a detectable loss of sulfate. The activity of sulfated oxides prepared from an amorphous oxide was noticeably lower; it depended only slightly on the temperature of calcination and sulfate sulfur content. The catalytic behavior of the sulfated oxide in both of the reactions is indicative of the absence of superstrong proton sites. Based on the results, assumptions on the nature of formed surface compounds were made.     

Properties of Zinc Oxide Adsorbent for Adsorbing Hydrogen Sulfide

Russian Journal of Applied Chemistry - The paper defines the conditions for the synthesis of hydrogen sulfide adsorbent based on zinc oxide from basic zinc carbonate in order to produce strong,...     

Mechanochemical Synthesis and Catalytic Properties of the Calcium Ferrite Ca2Fe2O5

The formation of the real structure of calcium ferrite prepared by the calcination of a mechanochemically activated hydroxide mixture at 600–1100°C was studied by X-ray diffraction analysis, electron microscopy, thermal analysis, Moessbauer spectroscopy, IR spectroscopy, small-angle X-ray scattering, and secondary-ion mass spectrometry. It was found that low-temperature calcium ferrite is an anion-modified oxide, in which the ordering of oxygen vacancies was incomplete. Regions with a disordered structure were detected on the surface of crystallites. As the calcination temperature was increased, the brownmillerite crystal structure was improved and the intercrystalline boundaries were formed and then annealed. At the surface, these processes were accompanied by a change in the predominant form of adsorbed NO from nitrosyl to dinitrosyl species. An increase in the specific catalytic activity of samples with calcination temperature can be associated with the perfection of the brownmillerite structure and with a change in the state of adsorption centers.     

Mechanochemical Synthesis of Nanosize Metastable Zirconium Oxide

The formation of oxide phases in the course of mechanical activation of amorphous zirconium hydroxide was studied.     

Effect of Photochemical and Reductive Activation of Titanium Dioxide on Its Catalytic Properties in Deposition of Metallic Copper

We have established that as a result of both photochemical and reduction heat treatment of titanium dioxide preparations impregnated with transition metal salts, there is an increase in their catalytic efficiency in the process of copper deposition. We consider reactions leading to activation and deactivation of the catalysts.     

Effect of Acid Modification on the Structure and Catalytic Activity of Aluminum Oxide

The effect of acetic acid introduced as modifying additive into active aluminum oxide on its structural characteristics is considered. A relationship is established between the structural characteristics, content and features of aprotic acid centers, and catalytic activity of the obtained catalysts in dehydration of methylphenylcarbinol.     

添加剂对铈锆复合氧化物性能的影响

制备了铈锆及含有氧化钇、氧化镧和氧化镨的铈锆复合氧化物,并用XRD和BET手段对新鲜及高温老化后的样品进行了表征.结果表明,制备的样品具有单一的立方晶相,并能耐较高的温度;同时,添加剂能增大铈锆复合氧化物的孔径,提高其耐热性能.     

Effect of Low-Temperature Heating on the Properties of Graphene Oxide Aerogel

The paper describes the effect of low-temperature annealing in air on the composition and structure of graphene oxide aerogel. It has been found that the concentration of carbon in the aerogel sharply increases, i.e., its carbonization occurs, already at a temperature of 175°C. At the same time, both the outer shape of the aerogel granules and the internal porous structure are preserved.     

Characterisation and Catalytic Properties of Vanadium Oxide Supported on Alumina Prepared by Sol-Gel Method

Vanadia-alumina xerogels were prepared by sol-gel method using organic precursors of metal and acetic acid as hydrolysis source. The purpose of this work is to study the change in the structure of dispersed vanadia as a function of preparation parameters, mainly the hydrolysis ratio k = [CH₃COOH]/[Al(O-s-Bu)₃] and the vanadium content V/V + Al (%).The amount of acetic acid affects considerably the solid texture, thus the pore size increases with the k ratio. In the same time, ⁵¹V NMR spectroscopy shows a decrease in the vanadium coordination from six-fold to fourfold. The investigation by temperature programmed reduction (TPR) shows that the reducibility of catalysts is determined in the order: K = 3 > K = 2 > K = 1. Furthermore, the catalytic activity in paraxylen oxidation follows a trend similar to that observed in TPR.The increase of vanadium content from 5 to 10%, favours the association of vanadium monomeric species, resulting in a new surface species. Hence, the coordination of vanadium changes from tetrahedral to octahedral, which induces a fall in partial oxidation selectivity.     

稀土元素镧对锌阳极带电化学性能的影响

研究了镧的加入对牺牲锌阳极带电化学性能的影响。结果表明，稀土元素镧对锌阳极带的电位和电流效率影响很小，实验结果符合相关标准。证明在纯锌中添加微量稀土元素镧改善锌阳极带机械性能，同时保持必要的电化学性能的工艺方法是有效、可行的。     

Mechanochemical Preparation of Nanodispersed Mo3@CeO2 Composite and Its Catalytic Properties in Oxidation of Ethanol

Theoretical and Experimental Chemistry - It was shown that mechanochemical treatment of 1 : 1 MoO3–CeO2 oxide mixture leads to the formation of nanosized particles with core–shell type...     

活化温度对CuBTC催化CO氧化反应性能的影响(英文)

考察了金属有机骨架材料CuBTC(BTC为均苯三酸)催化CO氧化的反应性能,发现CuBTC对CO氧化反应表现出良好的催化活性,且CuBTC样品的活化温度对其催化活性的影响很大.原位漫反射红外光谱、粉末X射线衍射、扫描电镜、热重分析和差示扫描量热结果表明,CO在CuBTC骨架中不饱和金属位点上的配位是加速CO氧化的主要原因,且这种不饱和金属位点越多,其催化活性越高.