Calcination temperature, effect oxide

Lanthanum oxide(99.9%) was dissolved in 1 1 HNO, solution and mixed with equal mol of FeCNO))) and then added complexing agent and dispersant( when needed) to malm a transparent solution. This solution was kept at 60-70 C to evaporate the water, and the viscous gel was formed through sol process. Kept the gel on water bath for 3-4h and then dried at 120 C, finally calcined in air at 650 C for 4h (except the calcination temperature effect study). 

Harper, F. C. (1967). Effect of calcination temperature on the properties of magnesium oxides for use in magnesium oxychloride cements. Journal of Applied Chemistry, 17, 5-10. 

Boccuzzi F, Chiorino A, Manzoli M, et al. 2001. Au/Ti02 nanosized samples A catalytic, TEM, and FTIR study of the effect of calcination temperature on the CO oxidation. J Catal 202 256-267. 

Larese, C., Lopez Granados, M., Mariscal, R. et al. (2005) The effect of calcination temperature on the oxygen storage and release properties of Ce02 and Ce—Zr—O metal oxides modified by phosphorus incorporation, Appl. Catal. B Environ., 59, 13. 

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... 

Figure 11 Effect of calcination temperature of the V-ion-implanted titanium oxide sample on the ESR spectra of + species in the V-ion-implanted titanium oxide photocatalyst at 77 K.

During the course of studying the effect of crystallite sizes, attempts were made to produce very small unsupported iron oxide powders by lowering the calcination temperature of the iron hydroxyl gel that was precipitated from iron nitrate with ammonium hydroxide. However, catalysts calcined below 300°C still contain hydroxide, and they show high selectivity in butadiene production. For this reason, two catalysts, calcined at 250°C and 300°C, respectively, were studied in more detail. 

The most obvious choice to determine phases that may be present in the molybdena catalyst is XRD. Matching of diffraction lines obtained for the catalyst with those of pure bulk compounds gives unequivocal identification of phases present. This is one of the few techniques that yields positive results. The absence of matching diffraction lines, however, is not proof that the phase in question is not present in the catalyst. The XRD technique is limited to particle sizes of above approximately 40 A for oxides or sulfides, lower sized particles giving no discernible pattern over that of the broad alumina pattern. Thus, the presence of a highly dispersed phase, either as small crystallites or as a surface compound of several layers thickness will not be detected. Also, if the phase is highly disordered (amorphous), a sharp pattern will not be obtained, although some broad structure above that of the alumina may be detected. It is a moot point as to whether such a case is considered as a separate phase or a perturbation of the alumina structure. Ratnasamy et al. (11) have examined their CoMo/Al catalyst from the latter point of view, with particular emphasis on the effect of calcination temperature. 

The situation with respect to reduction of the CoMo/Al catalyst is more confusing. Various authors claim that the presence of cobalt at a low level accelerates (16), retards (27), or has no effect on (31) the reduction of the molybdena. Of course, at high Co loadings, more reduction is obtained than for the Mo/Al alone, due to reduction of the Co304 phase present, but it is difficult to assess whether the molybdena is itself affected by the cobalt reduction. It is well known that transition metals can catalyze reduction of oxides (32). It is probable that the different results obtained could be due in large part to differences in preparation or calcination temperature as pointed out earlier. 

Oxide electrodes have been observed to be almost immune from poisoning effects due to traces of metallic impurities in solution [99]. This is undoubtedly due primarily to the extended surface area. It can be anticipated that the calcination temperature must have a sizable effect. But in addition, a different mechanism of electrodeposition must be operative. Chemisorption on wet oxides is usually weak because metal cations are covered by OH groups [479]. As a consequence, underpotential deposition of metals is not observed on Ru02, although metal electrodeposition does takes place. However, electrodeposited metals give rise to clusters or islands and not to a monomolecular layer like on Pt. Therefore, the oxide active surface remains largely uncovered even if metallic impurities are deposited [168]. Thus, the weak tendency of oxides to adsorb ions, and its dependence on the pH of the solution is linked to their favorable behavior observed as cathodes in the presence of metallic impurities. 

Benzylation of toluene with benzyl chloride, which is a typical example of Friedel-Crafts alkylation, is known to be catalyzed by Lewis-type superacids such as A1C13 and BF3. This type of catalyst has been mostly used for the Friedel-Crafts reaction, which is one of the most studied of organic reactions. This reaction was performed over several metal oxides and sulfates, and iron sulfates showed an unexpected effectiveness for the reaction (102-104). The catalytic activities of FeS04 and Fe2(S04)3 for the reaction were examined in detail the activities were remarkably dependent on calcination temperature, the maximum activity being observed with calcination at 700°C (105-107). Catalytic actions analogous to the above case were also observed with other Friedel-Crafts reactions, the benzoyl-ation of toluene with benzoyl chloride (108), the isopropylation of toluene with isopropyl halides (109), and the polycondensation of benzyl chloride UIO). 

Figure 2 shows the effectiveness of this procedure as a function of the preoxidation temperature. At 500°C preoxidation no difference is observed between either a He or H reduction. After a 600°C calcination the He reduction was less effective, especially for higher temperature peaks, and this difference was more pronounced after a 700°C calcination temperature. It is important to note that more than oxidation occurs at high temperatures, sintering of the Pt and dehydration of alumina also occur. However, it is not surprising that hard to reduce Pt occurs at the highest temperature of preoxidation. All these factors contribute to the change in the... 

The surface crystal structure and particle size can also influence photoelectro-chemical activity. The mode of pretreatment, for example, dictates whether titanium dioxide exists in the anatase phase (as is likely in samples which have been calcined at temperatures below 500 °C) or in the rutile phase (from calcination temperatures above 600 °C) or as a mixture of the two phases for pretreatments at intermediate temperature ranges. The effect of crystalline phase could be easily demonstrated in the photocatalytic oxidation of 2-propanol and reduction of silver sulfate, where anatase is active for both systems. But when the catalyst was partially covered with platinum black, alcohol oxidation was easy, but silver ion reduction was suppressed. On rutile, redox activity was observed for Ag+, alcohol oxidation was negligible [85]. 

The presence of different oxidation steps during coke burn can be related to the acidity of the support and the structure of the metallic phase. Barbier [13] has shown that the first oxidation zone at low temperatures corresponds to the carbonaceous materials on the metallic phase, whereas at high temperatures of oxidation are attributed to the coke on the acidic sites of the support. In our case, the total acidity varies in a wide range after calcination at 773 K. In fact, the NH3 uptake on alumina was 750 pmol/g catalyst, whereas on calcined niobia it was only 112 (.imol/g catalyst [5]. Moreover, according to Pittman and Bell [14], the acidic sites on a similar niobia support are basically weak Lewis sites. On the other side, coke burn in the neighboring of the metallic sites can be also associated to the promoting effect of platinum and the platinum-niobia interface. 

In order to give answer to these questions, this study presents data on the effect of WOx loading, calcination temperature, and preparation methodology on the characteristics of the W0x-Ce02 catalysts. If, indeed, the oxidative behavior is the one that promotes the isomerization, then the replacement of Zr02 with Ce02 should improve the performances of this catalyst in isomerization reactions. 

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... 

However, there is much that remains unknown and in particular it is not known how the above phenomenon (Eq. 14.12) reflects the catalyst performance. Fig. 14.10 shows the change in the rate constant k (mol s ) of the oxidation of phenol with the change in the Cu content. The rate constant (k) linearly increases with the Cu content regardless of the calcination temperature of the catalysts. Thus, the active component in CCi Cup g catalysts is Cu. In the subsequent work, they reported that sol-gel technique is better than co-precipitation method, and high dispersion of copper oxide phase on the cerium oxide causes high catalytic activity. They emphasized the importance of the combination of the mixed valence state of Ce and Ce caused by an incorporation of Cu, which causes the reversible addition and removal of oxygen in this inherently defect structure. Here, the defect structure in CeOj is also emphasized. However, their discussion is rather sophisticated and their claim on the inherent function of this catalyst is difficult to be understood. The clear point is that copper in this catalyst is considerably active and durable in the wet-oxidation condition due to the effect of CeO,. 

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