Calcination temperature, optimum

C02 — 12.5 mol % space velocity 6400 h 1, the CO conversion rate was found to depend very strongly on the calcination temperature of the catalyst. For example, a catalyst calcined at 500 °C achieved only 25% conversion by 350 °C, while a catalyst calcined at 900 °C achieved 80% conversion by 225 °C. The authors suggested that the Cu-Mn spinel oxide was more easily reducible after high temperature calcination treatment based on a TPR study, allowing for a greater number of highly dispersed Cu species, as verified by XRD. The optimum Cu/Mn ratio was found to be 1/2. 

Ermakova and co-workers manipulated the Ni particle size to achieve large CF yields from methane decomposition. The Ni-based catalysts employed for the process were synthesized by impregnation of nickel oxide with a solution of the precursor of a textural promoter (silica, alumina, titanium dioxide, zirconium oxide and magnesia). The optimum particle size (10 0 nm) was obtained by varying the calcination temperature of NiO. The 90% Ni-10% silica catalyst was found to be the most effective catalyst with a total CF yield of 375 gcp/gcat- XRD studies by the same group on high loaded Ni-silica... 

Crystallinity. It seems that the degree of crystallinity of Ti02 is an important factor in obtaining active Ti02 (46). Indeed, amorphous titania is poorly active. An optimum calcination temperature of amorphous samples presumably corresponds to a compromise between an enhanced crystallinity, together with a decreased density of lattice defects, and limited decreases in surface area and coverage by OH groups. 

Figure 17.1 summarizes the effect of the calcination temperature on the catalytic activity for butane isomerization over sulfated zirconias prepared from different zirconia gels dried at the optimum temperatures. The figure indicates that the maximum activities are approximately the same for different catalysts even though... 

The materials thus prepared were examined in the acid-catalyzed conversion of methanol into dimethyl ether. The conversions are shown as a function of calcination temperature of the catalysts in Figure 17.9. The highest activity for 40%- and 80%-WO3/SnO2 was observed at a calcination temperature of800°C, but materials with lower quanhties of W required higher temperatures of calcination for optimum achvity. This indicates the main tendency that the lower the quantity, the higher the temperature showing the optimum activity namely, 900, 1000, 1100, and 1150°C for the materials with 20, 10, 5, and 2% W, respectively. 

Removal of coordinating ligands by careful calcination prior to reduction, is therefore extremely important for metal/zeolite catalysts, because it controls the cation locations and thus the metal particle growth mechanism during subsequent reduction. It has been demonstrated that the ultimate metal dispersion depends on the temperature of the calcination (50,69,71,79,107). An optimum calcination temperature can be defined for obtaining maximum dispersion of metals in zeolites. 

Various reactions have been studied on mixed rare earth and the La and Ce forms. These include ethylation of benzene 18), propylation of toluene 14), o-xylene isomerization 21), butane cracking 14), cracking of n-hexane, n-heptane, and ethylbenzene (8), and isomerization and disproportionation of 1-methy 1-2-ethylbenzene (7). Other reactions are summarized by Venuto and Landis 18). In several reports, an optimum calcination temperature for best catalytic performance has been demonstrated (7, 8, 14, 18, 21). 

Fig. 2 shows (a) the dependence of the activity at 473 K upon the calcination temperatures of the precursor of copper and ytterbium oxide mixture, where the content of Yb is 14 atomic % to Cu and the precursors were reduced at 523 K, and (b) the XRD pattern of the precursor at various calcination temperatures. As shown in Fig. 1(a), the catalytic activity improved by the calcination of the obtained coprecipitate and the catalyst prepared from the precursor calcined at 473 K exhibit the optimum activity. The activities of the catalysts prepared from the precursor calcined above 473 K decreased with raising the calcination temperatures. From the XRD patterns of the precursors calcined at various temperatures as shown in Fig.2 (b), only the pattern attributed to CuO is observed to the precursors calcined up to 623 K and the peaks are sharper with raising the calcination temperatures, while the pattern attributed to 6203 is also observed to the precursors calcined over 723 K. These results suggest that the condition of the precursor of the oxide mixture is seriously affected by the catalytic behavior. This suggests that the condition of the oxide mixture is one of the important factors for the preparation of active catalysts from the mixture. The condition of the precursors was also observed by XPS. 

Table 4 shows the XPS peak intensity ratio of Cu (2p)A"b (3d) for the catalyst precursors, the content of Yb is 14 atomic %, calcined at various temperatures. From the results in Table 4, the values of the ratio decrease with raising the calcination temperatures. This suggests that ytterbium oxide gradually deposits over the surface when raising the calcination temperatures. Therefore, the optimum condition of the catalyst precursor. 

The purer grades of seawater magnesia have proved more difficult to densify during calcination owing to the lower concentration of mineralizing impurities. To overcome this difficulty, high-pressure pelletization of caustic-calcined magnesia is used. It has been demonstrated that there is an optimum calcination temperature for maximum fired density after... 

Table 1 presents the n-hexane conversion, selectivity to isomers and coke deposited after reaction for catalysts prepared by using two different platinum precursors tetraammine platinum nitrate and hexachloroplatinic acid. Both materials were calcined at different temperatures after platinum addition. For both platinum precursors, run under standard operational conditions, the optimum calcination temperature for catalytic activity was 500 °C. The amount of coke is small and the TPO profiles of the coked samples (not shown) are similar for all catalysts. Coke is completely burnt off at temperatures below that at which the catalyst was calcined after the metal addition. This is an important feature, because regeneration procedures would not affect the metal function. 

HAuChaq + NaOH [Au(OH)4] Na"aq (pH 6-10) Au(OH)3/Support wash, dry then calcinate at 563-673 K - AuNP/Support (optimal AuNP size 3 nm, stable hemispherical NPs, the size being controlled by the calcination temperature whose optimum is 570 K, optimal support Ti02 for which the addition of Mg citrate is necessary during or after co-precipitation for a good dispersion of hny AuNPs). 

Natesakhawat et al. [6] investigated Fe/promoter ratio, pH of precipitation medium, calcination, reduction temperatures and preparation methods on the catalytic activity of Fe-Al and Fe-Al-Cu catalysts. The WGS activity of Fe-Al catalysts increases with decreasing Fe/Al molar ratio and reaches a maximum at Fe/Al =10. Further addition of Al (Fe/Al = 5) causes a significant drop in the WGS activity. They also proposed that optimum pH value of the precipitation medium is 9 to get the highest activity of Fe-Al catalyst. The catalytic activity of Fe-Al catalysts is seen to go through a maximum at 450 °C calcination temperature and further increase in the calcination temperature results in a decrease in WGS activity possibly due to loss of surface area caused by sintering. 

The optimmn calcination temperature varies in different clay minerals. For sodium and calcium montmorrilonite a calcination temperatuie of 830 °C has been found to be optimal (He et al, 1996). Galal et al. (1990) reported the same optimmn temperatuie range—600-800 °C— for the calcination of kaohnite, montmorrilonite, and mixed type clays. He et al. (1995) found, for a series of different clay minerals, optimum calcination temperatures ranging between 650 and 960 °C (see Table 9.5). 

Table 13. Initial (TOS = 1 min) Conversion and Selectivity Obtained on S04 /Zr02 as a Function of Method of Sulfation (S = Sulfuric Acid, AS = Ammonium Sulfate) and Initial Concentration of Sulfur (6 and 9 wt% S04 , AS Method), at Their Respective Optimum Calcination Temperature...

Pure metal ferrite nanoparticles Optimum calcinations temperature (K) Optimum concentration of PVP (gm/ml) Optimum Heating rate (K/min) Optimum Calcinations Time (h)... 

Although the optimum cements (at four weeks) would indicate that AT-Ll (CI=2.03) requires a higher calcination temperature than PL-F104 (CI = 1.75) it should be remembered that Eckel stated that the higher... 

Tomishige et al found that cyclic carbonates such as EC and PC could be selectively synthesized over Ce02-Zr02 catalysts, via the reactions of CO2 with the respective glycol. No PC or dipropylene glycol was detected under the optimum reaction conditions. The 1,2-propylene glycol conversion was 2% and was much dependent on the composition and calcination temperature of the catalysts. 

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