Calcining, conditions

Catalyst performance depends on composition, the method of preparation, support, and calcination conditions. Other key properties include, in addition to chemical performance requkements, surface area, porosity, density, pore size distribution, hardness, strength, and resistance to mechanical attrition. 

On the other hand, if the stone is calcined under severe calcining conditions, ie, high temperature and long retention, the lime may become... 

Certain stifled calcination conditions can cause recarbonation in which CO2 is readsorbed on the lime s surface. This can seriously diminish the quahty and concentration of the lime. The possibiflty of recarbonation underscores the importance of rapid expulsion of the CO2 gas during calcination. 

Sodium tripolyphosphate is produced by calcination of an intimate mixture of orthophosphate salts containing the correct overall Na/P mole ratio of 1.67. The proportions of the two anhydrous STP phases are controlled by the calcination conditions. Commercial STP typically contain a few percent of tetrasodium pyrophosphate and some trimetaphosphate. A small amount of unconverted orthophosphates and long-chain polyphosphates also may be present. 

Cost and Quality. Many factors affect catalyst support cost including which raw materials are used, the purity of the raw materials, the chemical processing steps required, the fabrication method used, the severity of calcination conditions, and the extent of the quaHty assurance procedure. In... 

Sulphate process. The ilmenite is reacted with sulphuric acid giving titanium sulphate and ferric oxide. After separation of ferric oxide, addition of alkali allows precipitation of hydrous titanium dioxide. The washed precipitate is calcined in a rotary kiln to render titanium dioxide. The nucleation and calcination conditions determine the crystalline structure of titanium dioxide (e.g. rutile or anatase). 

Effect of the calcine condition on surface structure of titania nanocrystal photocatalyst... 

Homogeneous, nanosized, copper-loaded anatase titania was synthesized by an improved sol-gel method [197], These titania composite photocatalysts were applied to the photoreduction of carbon dioxide to evaluate their photocatalytic performance. Methanol was found to be the primary hydrocarbon product [198], Under calcination conditions, small copper particles are well dispersed on the surface of anatase titania. According to XAS and XPS analysis, the oxidation state of Cu(I) was suggested to be the active species for C02 photoreduction [199], Higher copper dispersion and smaller copper particles on the titania surface are responsible for a great improvement in the performance of C02 photoreduction. 

Composition (Na20 Si02 AI2O3 H2O template) Temperature (X) Time (h) Calcined condition Ref. 

New synthetic procedures used to crystallize VPI-5 are described. Mixtures of amines and quaternary ions are utilized to crystalize pure VPI-5. A low cost, high yield preparation involves the use of triisopropanol amine and tetramethylammonium hydroxide. Some samples of VPI-5 can be transformed into AIPO4-8 upon certain calcination conditions. Extensive washings of the aforementioned, as-synthesized VPI-5 yields a product which does not transform into AIPO4-8. 

To prepare noble metal on H-mordenite catalysts the noble metal ammino complex-containing material is normally heated in air using staged heating (21, 22, 23, 24). In Ref. 24 the calcination of Pt(NH3)4-NH4 mordenite is discussed in detail, and it is shown that during calcination in air at about 300° C a strongly exothermic reaction occurs, presumably a result of the oxidation of NH3. Data are presented on the influence of calcination conditions on platinum dispersion. 

The appearance of the hydroxyl bands at 3650 and 3550 cm-1 upon heating the ammonium form accompanies the decrease and disappearance of the NH-stretching bands as ammonia is evolved. The rate of decomposition of the ammonium ions appears to be influenced by the calcination conditions. Ward observed that most of the ammonium ions decomposed between 200° and 350°C, and at 420° only discreet hydroxyl bands were present (148). With extensively exchanged samples (>90% of the exchange sites occupied by ammonium ions), the 3550-cm I band was more intense than that at 3650 cm-1, in contrast to the intensity relationship observed at lower ammonium-exchange levels. Angell and Schaffer also noted the variability of the relative intensities of the two bands with different extents of ammonium ion exchange. 

The reappearance of Brdnsted acid sites has been observed for the high calcined nickel-molybdenum-alumina catalysts. The presence of a nickel aluminate phase has been concluded from the reflectance spectra. The second Lewis band (1612 cm l) has a very low intensity, in comparison with the cobalt containing catalysts of a same composition and after the same calcination conditions. 

Choudhary V. R. and Pandit, M. Y. Surface properties of magnesium oxide obtained from magnesium hydroxide - influence on preparation and calcination conditions of magnesium-hydroxide. Appl. Catal., 1991, 71, 265-274. 

The chosen catalytic test reaction was the oxidation of phenol, which yields a mixture of catechol, hydro-quinonc, and 1,4-benzoquinone (Scheme I). The reaction was conducted at atmospheric pressure by continuously adding aqueous H2O2 to a mixture of catalyst, phenol, water, and a solvent (either methanol or acetone) at the reaction temperature (usually 373 K) reaction times were l-4h. Conversions and product sclectivities depended on the composition of this mixture under the best conditions, H2O2 conversion was 100%, phenol conversion 27%, and phenol hydrox-ylation selectivity 91%. The ratio of o />-substituted products (Scheme 1) was usually about unity. It was concluded that catalytic performance depended critically on calcination conditions, i.e. on the completeness of removal of the template. Many facets of the reaction remain to be investigated. 

The C0O/AI2O3 catalyst of this example [3] was prepared by pore volume impregnation of AI2O3 with Co(N03>2 followed by drying and calcination (heating in air). It appeared that calcination conditions are critical. For instance, the colour of the sample depends strongly on the calcination temperature. 

Cadmium pigments have been manufactured by both a direct calcination process and a precipitation-calcination process. In the first instance, a mixture of cadmium carbonate and sulfur (and zinc oxide and selenium if the hue to be produced requires their addition) is calcined at 520-600°C for 1-2 h. This direct calcination process is complicated by the volatility of cadmium oxide and selenium, both of which are toxic and require special handling. In the precipitation process, an alkali sulfide solution is added to a solution of cadmium and (in the case of green-shade yellows) zinc salts or to a solution of cadmium and (in the case of deep oranges, reds, and maroon) selenium metal to precipitate the appropriate compound. The precipitate is washed, dried, and calcined at 600-700°C in an inert or reducing atmosphere to convert the precipitated cubic structure to a more stable wurtzite crystal. The calcination conditions control particle size, which ranges from 0.2 to 1.0pm. 

Catalyst calcination conditions are additional critical preparative variables that have a significant impact on the structure as well as the catalytic performance of Mo V-Te-Nb oxide catalyst. From one precursor, two catalysts of very different crystal phases are obtained under different calcination atmospheres. The catalyst calcined in nitrogen flow exhibits a high catalytic performance. In contrast, catalyst calcined in air is inactive toward propane oxidation. 

The catalytic activity of SO jT rOj varies with the type of zirconia gel and the drying and calcination conditions. The calcination temperature showing the maximum activity and acidity often varies with the type of prepared gel. For instance, the maximum activity for the conversion of butane to isobutane is observed with calcination at 575 and 650 °C, respectively, for the materials prepared from Zr0(N03)2 and ZrOCh as starting reagent [32]. 

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