Calcination effect, hydrocarbon

Chromium zeolites are recognised to possess, at least at the laboratory scale, notable catalytic properties like in ethylene polymerization, oxidation of hydrocarbons, cracking of cumene, disproportionation of n-heptane, and thermolysis of H20 [ 1 ]. Several factors may have an effect on the catalytic activity of the chromium catalysts, such as the oxidation state, the structure (amorphous or crystalline, mono/di-chromate or polychromates, oxides, etc.) and the interaction of the chromium species with the support which depends essentially on the catalysts preparation method. They are ruled principally by several parameters such as the metal loading, the support characteristics, and the nature of the post-treatment (calcination, reduction, etc.). The nature of metal precursor is a parameter which can affect the predominance of chromium species in zeolite. In the case of solid-state exchange, the exchange process initially takes place at the solid- solid interface between the precursor salt and zeolite grains, and the success of the exchange depends on the type of interactions developed [2]. The aim of this work is to study the effect of the chromium precursor on the physicochemical properties of chromium loaded ZSM-5 catalysts and their catalytic performance in ethylene ammoxidation to acetonitrile. 

Effect of Calcination on Activity and Selectivity to Hydrocarbon and C02 of FTS over 15% Co/Si02... 

Mica platelets can be coated with a variety of other compounds to produce further pigments. Solid-state reactions and CVD processes extend the possibilities for the synthesis of mica pigments. In addition, the calcination of the materials in the presence of inert (e.g., N2, Ar) or reactive gases (e.g., NH3, H2, hydrocarbons) allows the formation of phases, which carmot be produced by working in air. Table 5.17 contains a summary of mica-based effect pigments with special coloristic properties. 

Apatitic rock phosphates (a poor-quality phosphate) are commonly calcined in fluidized beds (with one, two, or even three stages) to remove impurities (carbonates, water, and organic matter) and to increase phosphorus concentration. The hydrocarbon content (up to 5%) of this phosphate provides most of the heat needed for calcination. Increasing the process temperature improves the upgrading of the ore, but decreases the agronomic effectiveness in direct application to soils. This operation has a maximum temperature of -900°C.P°l... 

Manganese oxides have long been known to be catalysts for a variety of gas clean-up reactions. Manganese/copper mbced oxide (Hopcalite) is the catalytically active component in gas mask filters for CO CO is converted to CO2 at room temperature [4]. Further applications of manganese oxide catalysts are the NH3 oxidation to N2 [5], the combustion of VOC [6,7] and methane [8], the oxidation of methanol [7], the O3 decomposition [9] and the NOx reduction [14]. Perovskite-type oxide catalysts (e.g. LaMnOs) have been proven to be effective catalysts for the total oxidation of chlorinated hydrocarbons [10]. Several studies have shown that besides preparation method and calcination temperature the kind... 

In the present study Ru-Sn/Al203 catalysts were calcined in air and reduced under H2 flow at various temperatures. The effect of calcination temperature on the performance of catalysts is shown in Table 4. Calcination was performed for 4 h at the specified temperatures. After calcination the catalysts were subsequently reduced tmder the flow of H2 at 350 °C for 4 h. Results listed in Table 4 indicated that the calcination temperature hardly affected the conversion of EL, while it showed clear influence on the product selectivity. Upon increasing the calcination temperature the selectivity of ROH passed through a maximum at 350 °C. Appreciable selectivity of hydrocarbons along with conparatively lower selectivity of ROH over the catalysts, calcined at 250 °C or at a lower temperature, can be explained by a large amount of residual chlorine. On the other hand, calcination of the catalyst at 400 °C or at a higher temperature may result in the segregation of surface Ru and Sn species, and hence lower selectivity of ROL [4],... 

On dechlorinated samples, calcination at 500°C before hydrocarbon oxidation induces an inhibiting effect on ceria containing catalysts for propene oxidation (Fig la). On the other hand, the inhibiting effect of ceria appears already after reduction for propane oxidation (Fig lb)... 

Opal in which brilliant colors appear against a dark background are the most valuable and probably the least understood. The effect is not entirely that of a dark substrate but may also involve a phenomenon similar to that of a light trap like a bundle of needles viewed from the points. There are no doubt other effects as well, such as a dark material scattered through the matrix. For example, black opals were examined by Mitsyuk et al. (357). The dark organic material in the pores was found to resemble a hydrocarbon. After calcination the decolorized opal- increased in density from 2.0 to 2.2 g cm as organic matter and water were removed. The microstructure of opal has been described in further detail by Sanders and Darragh... 

It is well admitted that the first step of the hydrocarbons synthesis from syngas is the CO dissociation on a metallic center (Co°, Fe°, or Co-Fe in the present case). CO dissociation into Cgurf and CO2 has been studied on the partially Lai j,Coo.4Feo,603 5 solids [43]. The results clearly show that the rate of CO dissociation increases almost linearly with the lanthanum deficiency. This is associated with the increased amount of reduced metal (2.1 wt% for y = 0-10.9 wt% for y=0A). The metal particles size has also an effect. For y = 0.4, CO dissociation is lower when catalysts were initially calcined at 900 °C (12% of CO conversion for 14.1 wt% of metal of average particle size of 28 nm) compared to those calcined at 750 °C (19% of CO conversion for 10.9 wt% of metal of average particle size of 10 nm). The larger size of particles led to a lower surface/volume ratio and to a decrease of CO dissociation. 

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