Bismuth oxide based ceramics with improved electrical and mechanical properties:Part I. Preparation and characterisation

A study of the preparative variables in the synthesis of ceramics based on Bi2O3-Er2O3 solid solutions has shown that the best results are obtained with a coprecipitation method. Critical parameters in the synthesis are found to be i) wet milling of the precalcined powder with an appropriate liquid and ii) calcining and sintering temperatures. With the proposed method it is possible to produce monophasic, contamination free, dense and machineable ceramics suitable for practical applications

Structure and texture of aluminas

DelftChemTechApplied Science

Bereiding van fructose

Document(en) uit de collectie Chemische ProcestechnologieDelftChemTechApplied Science

The catalytic oxidation of 1-butene over bismuth molybdate catalysts : II. Dependence of activity and selectivity on the catalyst composition

The dependence on the composition of the oxide catalyst of the rate and selectivity of the oxidative dehydrogenation of 1-butene to butadiene over Bi2O3MoO3 catalysts has been investigated. The rate appears to be mainly determined by the Bi/Mo ratio and is optimal at Bi/Mo=1. This optimal composition is not connected with the presence of a particular compound in the binary oxide system: all compounds identified so far are either less active or not active at all. The activity pattern is complicated by a sintering reaction that differs in intensity in various ranges of the composition. The selectivity is mainly decided by the occurrence of the double-bond isomerization. This is more developed at lower temperatures and in the MoO3-rich compositions. It is considerably inhibited by a high-temperature pretreatment of the catalyst. The promoter action of Bi3+ is explained by the assumption of an enhanced tendency to dehydroxylation of the surface, thereby leading to the formation of anion vacancies that serve to accept the intermediate allylic structure. Formation of this structure is further assumed to be possible only if it becomes p bonded to Mo, thus explaining the advantage of the simultaneous presence of Bi and Mo

Catalytic oxidation of 1-butene over bismuth molybdate catalysts : I. The system Bi2O3-MoO3

In the system Bi2O3---MoO3 the following compounds were identified: 1. (1) Bi2O3 · 3MoO3 = Bi2(MoO4)3 m.p. 676 °C 2. (2) Bi2O3 · MoO3 = Bi2MoO6 = (BiO)2MoO4 m.p. 938 °C 3. (3) 3Bi2O3 · MoO3 = Bi6MoO12 m.p. 995 °C These compounds were found by investigation of the phase diagram of the Bi2O3---MoO3 binary system by means of thermal analysis. X-ray studies of sintered mixtures in this system confirmed the existence of the three compounds. A compound Bi2O3 · 2MoO3 could not be detected

Catalytic oxidation of 1-butene over bismuth molybdate catalysts : III. Reduction of bismuth oxide, molybdenum oxide, bismuth molybdate, and of some nonstoichiometric molybdenum oxides with 1-butene

The reaction of 1-butene with bismuth molybdate, MoO3, and some nonstoichiometric Mo oxides was studied as a function of time and temperature at virtually constant hydrocarbon pressure. The reaction proceeds to four-valent molybdenum and to zero-valent bismuth. It is initially fast on bismuth molybdate, but MoO3 and some of the nonstoichiometric oxides show an induction period. The hydrocarbon products of the reduction are butadiene, CO, and CO2, while also isomerization of 1-butene to cis- and trans-2-butene is observed. The kinetic analysis of the rate as a function of the time was made on the basis of a model proposed by Crank and extended by Haul, Just, and Dümbgen, consisting of a surface reaction followed by oxygen vacancy diffusion in the solid. The model furnishes quantitative values for a surface rate constant and a diffusion constant in the interior. The surface reaction was observed to be fast enough to account for the rate of the oxidative dehydrogenation. Since also the nature of the reduction products is similar to that observed during the catalytic reaction it is concluded that the latter consists of a surface reduction followed by a reoxidation with gaseous oxygen. The diffusion constants observed could be given as log D = log D0 - ED/RTBismuth molybdate log D0 = -3.73 ED = 29.3 kcal mole-1 MoO3 log D0 = -5.62 Ed = 22.1 kcal mole-1 The numerical values for D observed for the MoO3 reduction are equal to those obtainable from the experiments of von Destinon-Forstmann for the reduction of MoO3 by hydrogen

Catalytic oxidation of 1-butene over bismuth molybdate catalysts : III. Reduction of bismuth oxide, molybdenum oxide, bismuth molybdate, and of some nonstoichiometric molybdenum oxides with 1-butene

The reaction of 1-butene with bismuth molybdate, MoO3, and some nonstoichiometric Mo oxides was studied as a function of time and temperature at virtually constant hydrocarbon pressure. The reaction proceeds to four-valent molybdenum and to zero-valent bismuth. It is initially fast on bismuth molybdate, but MoO3 and some of the nonstoichiometric oxides show an induction period. The hydrocarbon products of the reduction are butadiene, CO, and CO2, while also isomerization of 1-butene to cis- and trans-2-butene is observed. The kinetic analysis of the rate as a function of the time was made on the basis of a model proposed by Crank and extended by Haul, Just, and Dümbgen, consisting of a surface reaction followed by oxygen vacancy diffusion in the solid. The model furnishes quantitative values for a surface rate constant and a diffusion constant in the interior. The surface reaction was observed to be fast enough to account for the rate of the oxidative dehydrogenation. Since also the nature of the reduction products is similar to that observed during the catalytic reaction it is concluded that the latter consists of a surface reduction followed by a reoxidation with gaseous oxygen. The diffusion constants observed could be given as log D = log D0 - ED/RTBismuth molybdate log D0 = -3.73 ED = 29.3 kcal mole-1 MoO3 log D0 = -5.62 Ed = 22.1 kcal mole-1 The numerical values for D observed for the MoO3 reduction are equal to those obtainable from the experiments of von Destinon-Forstmann for the reduction of MoO3 by hydrogen