Tatyana P. Minyukova

Dehydrogenation of methanol over copper-containing catalysts

Abstract The catalytic properties in methanol dehydrogenation of copper metal formed as a result of reduction by hydrogen of copper-containing oxides with different structure: copper chromite (tetragonally distorted spinel), copper hydroxysilicate (Chrysocolla), and copper-zinc hydroxysilicate (Zincsilite) have been studied. This process proceeds via successive reactions: (I) 2CH 3 OH=CH 3 OOCH+2H 2 and (II) CH 3 OOCH=2CO+2H 2 . The methyl formate selectivity for the catalysts studied was close to 1.0 at low methanol conversion, X ≤0.1, where the dehydrogenation process is represented by reaction (I), occurring far from its equilibrium. At 0.2≤ X ≤0.55, the selectivity decreases with increasing conversion, and the ratio of the activities in successive reactions may serve as a comparative characteristic for the catalysts. At high conversions, when reaction (I) is close to its equilibrium, selectivity is independent of the properties of studied catalysts and depends on the methanol conversion. Reaction (I) shows low sensitivity to the state of metal copper of reduced catalysts and, hence, low sensitivity to the composition and structure of oxides-precursors. The catalysts’ activity in reaction (II) greatly depends on the state of metal copper in the catalysts. It was assumed that the catalyst activity in methyl formate conversion to CO and H 2 and, hence, the selectivity of methanol dehydrogenation with respect to methyl formate in the region of moderate methanol conversion depends on the strength of interaction between metal copper particles and catalyst oxide surface, which is determined by the composition and structure of oxide-precursor.

Peculiarities of formation of ZnO and CuO-based solid solutions

Low-temperature (623 K) treatment of hydroxocarbonate compounds of copper-zinc and copper-zinc-aluminium leads to the formation of phases with CuO and ZnO structures, which are solid solutions of the promoter ions. The formation of solid solutions is attributed to structural distortions (uniform or local) in the oxide lattice due to the incomplete removal of OH− and CO32− groups at low temperatures.AbstractПоказано, что низкотемпературная обработка (623 К) гидроксокарбонатных соединений меди-цинка и меди-цинка-алюминия приводит к образованию фаз со структурами CuO и ZnO, представляющих собой твёрдые растворы промотирующих ионов. Сделано прелположение, что образование твёрдых растворов есть результат искажения (равномерного или локального) структуры окисла-матрицы за счёт неполного удаления OH3−−-групп при низких температурах.

Nature of the active component of copper-zinc-aluminium catalyst for methanol synthesis

Comparative studies of the catalytic properties and thermal stability of a copper-zinc-aluminium catalyst and its components have revealed that the catalytic activity is determined by a solid solution of copper and aluminium in zinc oxide containing OH− and CO32− groups in its anion skeleton. The presence of aluminium in the solid solution ensures the increase of the catalyst thermal stability in the reaction medium.AbstractИз результатов сравнительного исследования каталитических свойств и термоустойчивости медь-цинк-алюминиевого катализатора и фаз его составляющих следует, что каталитическая активность определяется твёрдым раствором меди и алюминия в окиси цинка, содержащим в анионном каркасе OH− и CO32−-грушы. Наличие алюминия в твёрдом растворе обеспечивает увеличение термоустойчивости катализатора в реакционной среде.

Non-hydrothermal synthesis of copper-, zinc- and copper-zinc hydrosilicates

Abstract Cu/SiO2, Zn/SiO2 and Cu-Zn/SiO2 samples have been prepared by the homogeneous deposition-precipitation method. The samples were analyzed by thermal analysis, X-ray diffraction and infrared spectroscopy after various heat treatments and compared with data obtained for several minerals. It has been shown that interaction between the components occurs through formation of hydrosilicates. Copper-silica system at a Cu:Si ratio ≤ 1, gives rise to a hydrosilicate stable up to a calcination temperature of 930 K resembling the mineral Chrisocolla; at higher ratios a hydroxonitrate (gerhardite type) is also formed. Zinc-silica interaction produces two hydrosilicates such as a well crystallized Hemimorphite at Zn:Si = 2 and highly dispersed Zincsilite at Zn:Si ≤ 0.75, both stable up to 1073 K. The Zincsilite structure consists of three layered sheets (an octahedral layer sandwiched by two tetrahedral ones) like the Stevensite mineral group. For the copper-zinc-silica system no copper hydrosilicate is formed. Copper merely enters the Zincsilite structure independenly of the applied (Cu + Zn):Si ratio. Resulting layered copper-zinc hydrosilicate may be described by formulaZnx-yCuy(Zn3-x–zCuz–y▪x)[Si4O10](OH)2.nH2O,where Zn3-x-zCuz-y– ions are located in octahedral sites, Znx-yCuy–ions in the interlayer; ▪x are vacancies in the layers. Copper and zinc in excess of the Zincsilite ratio of Me:Si = 0.75, gives rise to copper and copper-zinc hydroxonitrates.

STATE OF COPPER-CONTAINING CATALYST FOR METHANOL SYNTHESIS IN THE REACTION MEDIUM

Hydrogen interaction with solid solutions of the composition Cu0.08Zn0.02O* and Cu0.15Al0.10Zn0.75O* has been studied. It is shown that at catalytic temperatures the surface of anion-modified zinc oxide contains epitaxially bonded metallic copper particles. Reversibility of this phenomenon upon removing hydrogen indicates that in hydrogen medium a complex system consisting of the oxide stabilized by protons and epitaxially bonded with oxide metal copper particles formed.

Electron spectroscopic studies of copper in catalysts for methanol synthesis

The state of Cu2+ ions in Cu−Zn−Al catalysts for methanol synthesis has been studied by electron spectroscopy (5000–50000 cm−1). It has been established that low-temperature ZnO stabilizes copper in a distorted octahedral coordination as cluster structures resembling (but not similar to) CuO. The presence of Al promotes the formation of these clusters and inhibits the formation of CuO.AbstractВ работе методом электронной спектроскопии (5000–50000 см−1) изучено состояние ионов Cu2+ в Cu−Zn−Al катализаторе синтеэа метанола. Показано, что низкотемпературный ZnO стабилизирует медь в искаженно октаэдрической координации в виде кластерных структур, приближающихся (но не равных) к CuO. Присутствие алюминия способствует образованию таких кластеров, и препятствует образованию CuO.

Copper ions distribution in synthetic copper-zinc hydrosilicate

Abstract Copper ions distribution in the structure of synthetic copper-zinc hydrosilicate of zincsilite structure, obtained non-hydrothermal synthesis have been studied. Zinesilite is referred to the layered silicates of smectite group and is described by the formula Znx (Zn3-x▪x) [Si4O10](OH)2.nH2O, where Zn3-x – are the ions located in the octahedral positions of layers, formed by two sheets of [Si4O10] tetrahedrons; Znx are zinc ions in the interlayer; ▪x are the cation vacancies. Two types of copper ions were distinguished in accordance with the character of their interaction with hydrogen: (1) – substituting zinc ions in the octahedral positions of layers; (2) – substituting zinc ions in the interlayer. These two types of copper ions display the following properties when reacting with hydrogen: (1) – copper ions in octahedral positions start to be reduced at temperatures 553–573 K, and at 723 K reduction degree is 50% ; (2) – copper ions from interlayer start to be reduced at 503–533 K with a constant energy of activation, and their reduction may be complete at this temperature.

Physico-chemical studies of the temperature range for the formation of anion-modified oxides

The effect of metal ions on the temperature range for the exstence of anion-modified oxides formed during the formation of Mg and Zn oxides and solid solutions of Cu, Al, Cr and Ni ions in these oxides through thermal decomposition of the respective hydroxo compounds, has been established.AbstractОбнаружено влияние ионов металла на температурную область существовния анионно-модифицированных оксидов, образующихся при формировании оксидов Mg и Zn, твердых растворов Cu, Al, Cr, и Ni в них путем терморазложения соответствующих гидроксосоединений.

Phase transformation in the cupric magnesium oxide system

Due to the incomplete removal of OH groups, dehydration at 500°C of solid solutions of magnesium ions in Cu(OH)2 and of copper ions in Mg(OH)2 formed by coprecipitation leads to the formation of nonequilibrium cupric magnesium oxyhydroxide compounds with the structures of CuO and MgO, respectively. As a result of high-temperature dehydration, cupric oxide and solid solutions are formed in which up to 20 at. % of magnesium in MgO is replaced by copper ions.AbstractДегидратация соосаждённых твёрдых растворов ионов магния в Cu(OH)2 и ионов меди в Mg(OH)2 при 500°C приводит к образованию в результате неполного удаления OH-групп неравновесных медномагниевых оксогидроокисных соединений со структурами типа CuO и MgO соответственно. В результате высокотем-пературной дегидратации образуются окись меди и твёрдые растворы замещения до 20% ионов магния ионами меди в MgO.

DISTRIBUTION PECULIARITIES OF ZINC IONS IN OXIDES

Studies of the radial distribution of atoms indicate that upon calcining zinc hydrocarbonate at temperatures of 573 and 1273 K, the product oxide contains 5 and 1.5% zinc ions in octahedral interstitial sites, respectively. An imperfect structure is likely to result from the distortion owing to the incomplete removal of OH− and CO3− groups from the anion shell of zinc oxide.AbstractМетодом радиального распределения атомов показано, что при прокаливании гидрокарбоната цинка при температурах 573 и 1273 К образующийся оксид содержит соответственно 5% и 1,5% ионов цинка в октаэдрических междоузлиях. Формирование дефектной структуры, по-видимому, связано с искажением структуры за счёт неполного удаления OH− и CO3−-групп из анионного каркаса оксида цинка.