Oxides preparation methods comparison

Several preparation methods have been reported for the synthesis of TS-1. In this work, we have investigated the physicochemical properties of TS-1 samples synthesized by different preparation metiiods and tested these materials as catalysts for the oxidation of n-octane, 1-hexene and phenol using aqueous hydrogen peroxide (30 wt%) as oxidant at temperatures below 100 C. For comparison, Ti02 (anatase) and the octahedral titanium-containing silicate molecular sieve (ETS-10) (5) have been studied. The effect of the presence of aluminum and/or sodium on the catalytic activity of TS-1 is also discussed. 

Spinel oxides are important industrial catalysts, possessing good thermal and chemical stability and an ability to maintain catalytic activity at high temperatures. The study reported here is concerned with the properties ofZn(II)-Cr(III) spinel oxides prepared from a carbonate containing LDH precursor. For this study the spinel oxide was separated, by treatment with dilute mineral acid, from the oxide mixture (ZnO and ZnC O, ) obtained by the thermal decomposition of LDH. For comparison, Zn(II)-Cr(lII) spinel oxides were also prepared by more standard synthesis methods. Structural and textural properties were evaluated, using PXRD, TG/MS, FT-IR and N2 adsorption. 

Voigt [1705] prepared transparent Ge02 glasses on hydrolysis of Ge(OEt)4 the temperature of glass formation is about l(XfC lower in comparison with that used in conventional methods. On crystallization of amorphous oxide prepared on hydrolysis of Ge(OPri)4, a mixture of two phases, crystoballite and a-quartz, is formed. On further thermal treatment, phase transition of crystoballite to a-quartz occurs, while grinding in air results in the transition to a rutile-type structure on treatment at temperatures higher than 1050°C all phases are tranferredto a-quartz [1766]. 

Comparison of the existing data on the distribution of inorganic sulfur intermediates in the Black Sea anoxic zone [33,61,63-65] shows a confused picture, which may reflect both the non-equilibrium kinetics of chemical transformations within the sulfur cycle and the differences in methods employed. Future progress in the field will depend on the advance in analytical techniques capable of producing reliable data for individual sulfur intermediates in natural waters at low concentrations, and on sampling and preparation methods without oxidation artifacts. 

Mixed oxide samples were prepared by the co-precipitation from aquatic solutions of the cations ([Ce(IV)] = 0.1 M) by adding equal volume of 1 M NHj solution under controlled conditions. Further calcium cerium mixed oxide samples were prepared by the incipient wetness method, for comparison. The solid phase was heated to dryness, in an oven at 250 C. Samples of magnesium cerium and calcium cerium mixed oxide prepared by co-precipitation were subsequently calcined at 400, 600 and 800 "C. 

New Fe-Mo-Ti mixed oxides prepared via the sol-gel method comparison of the textural properties with solids obtained by impregnation... 

A COMPARISON OF IRON MOLYBDATE CATALYSTS FOR METHANOL OXIDATION PREPARED BY COPRECIPTATION AND NEW SOL-GEL METHOD... 

As we have outlined in the preceding discussion, the presence of different metal ions leads to strong differences in the final heating temperature for obtaining a single perovskite phase. Consequently, comparison of the performance of different preparation methods is possible only when data are available concerning the preparation of a specific mixed oxide by different methods. Unfortunately, scarce examples exist in the literature in this respect. In the following, some of these will be discussed. 

The physico-chemical properties of the supports and vanadium oxide catalysts are listed in Table 2. The catalysts are labeled XVj/M, where X corresponds to the % by weight of vanadium, V to vanadium, p to the preparation method (imp=impregnation, graf=grafting) and M to the support. No marked effect of the deposition of titanium oxide on the specific surface area of the silica was detected in the case of the support TSm, while, in the case of the vanadium-based catalysts, a decrease in Sbet was observed. The vanadium surface densities are calculated as number of vanadium atoms per square nanometer of catalyst (V/nm oat) to facilitate a comparison of the samples prepared on different surface area supports [6]. The vanadium contents of the samples are quite smaller than the theoretical monovanadate monolayer coverage of 2.3 VO,/nm" [6]. 

Phosphate and sulphate modifiers were incorporated by the addition of appropriate amounts of 0.01 M sulphuric or phosphoric acid to a pre-calcined aerogel followed by further calcination at 873 K. Samples are labeled as X-SiZr (y) where X refers to either sulphated (S) or phosphated (P) samples, and y refers to the mole ratio of sulphate/phosphate relative to zirconium in the preparation method. For comparison purposes, samples of zirconia and sulphated zirconia were also prepared. This was achieved via precipitation from zirconium isopropoxide (Aldrich 70 wt.%). The same H2O Zr propanol ratios were employed as used during the preparation of the mixed oxides. A sulphated zirconia, prepared by the use of sulphuric acid as hydrolysis catalyst was prepared for comparative purposes and had a nominal S Zr ratio of 0.30 1. A further sample was prepared where segregation of components was induced by thermal treatment by calcination at 1373 K for 6 h.of the non-treated SiZr (0)... 

Syntheses and characterizations of aniline/butylthioaniline copolymers comparisons of copolymers prepared by the new concurrent reduction and substitution route and the conventional oxidative copolymerization method. J. Polym. Sci. Polym. Chem., 43,1767-1777. 

Confusion in SMO literature can arise because there is no generally accepted method for determining surface density. As the metric that characterizes the surface oxide of supported metal oxide catalysts, surface density allows one to consider the various structures of the surface oxide on a common scale, independent of total oxide content, preparation method, calcination treatment, and surface area of the support oxide. Surface saturation and monolayer coverage are important threshold surface density values, at which surface oxide crystals form and at which complete consumption of surface hydroxyl groups of the support oxide occurs, respectively. Inconsistencies in these values come about because of (1) differences in their definitions, (2) difficulties in compatibilizing data from different characterization techniques, and (3) the use of support surface area instead of the overall composite SMO. These inconsistencies can make structural comparison of the same SMO composition, such as WO /ZrOj, difficult across different research groups. Calculated properly, however, the surface density metric provides the most simple and useful basis for understanding the relationship between surface nanostructure and catalytic and surface properties. 

Characterization of Ce02-Zr02 mixed oxides comparison of the citrate and sol-gel preparation methods. Chem. Mater., 15, 395-403. 

Synthesis of single-phase Au-Pd catalysts exhibited higher activity and reusability than random Au-Pd catalysts in the selective oxidation of glycerol. By comparison, the catalytic performance of Au-Pt and Au-Pd single-phase catalysts in the selective oxidation of various primary alcohols (benzyl alcohol, cinnamyl alcohol and 1-octanol), showed that Au-Pd catalysts were far more active than Au-Pt catalysts (Eq. 22.13). A significant improvement in catalytic activity was found when water, instead of toluene, was used as a solvent, with TOF values increasing by a factor of 1.5-6. Moreover, using the same preparation method, they demonstrated... 

Comparison of two preparation methods (impregnation and sol-immobilisation methods) for the synthesis of Au-Pd-supported catalysts in the liquid-phase oxidation of glycerol led to the conclusion that high activity coupled with high selectivity to the desired product (glycerate) can be achieved by gold-rich surface bimetallic nanoparticles with a mean particle size of 3-5 nm and metallic oxidation state. 

The preparation methods for the synthesis of unsaturated and saturated polyester resins were also elaborated for micro-wave conditions. In the polyaddition reactions of alkylene oxides (i.e., epichlorohydrin) and acid anhydrides (i.e., maleic and phthalic anhydrides), unsaturated polyesters were prepared in the presence of lithium chloride as a catalyst (Figure 30). In comparison with polycondensation reactions of acid anhydrides with diols, these reactions proceed without the release of by-products. 

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