Composition and pretreatment

Wilson, M. A. Combe, E. C. (1991). Effects of glass composition and pretreatment on the reactivity of a novel glass polyalkenoate (glass ionomer) dental cement. Clinical Materials, 7, 15-21. 

Effect of Composition and Pretreatment on Coke and H2 Selectivity. We examined the effect of catalyst composition and pretreatment on the selectivity for coke and H2. Results (Figures 5 and 6) indicate higher yields of coke and H2 at constant conversion for SA-59 relative to catalysts with lower alumina content. Pretreatment conditions influenced coke, H2 yields indirectly by influencing surface area and gas oil conversion. Thus, coke and H2 selectivity was not influenced by pretreatment conditions. We conclude that coke and H2 selectivity does not correlate with the concentration of A1 species of a particular coordination (eg., tetrahedral). 

Olthof B., Khodakov, A., Bell, A.T. and Iglesia, E. (2000) Effects of Support Composition and Pretreatment Conditions on the Structure of Vanadia Dispersed on Si02, AI2O3, Ti02, Zr02, and Hf02. Journal of Physical Chemistry E, 104 (7), 1515-28. 

The site of each reaction should be identified as well as possible. This is commonly done by experiments with various amounts of surface or catalyst in the reactor, or with various surface compositions and pretreatments. For the chain reaction of hydrogen with chlorine. Pease (1934) included experiments with added oxygen as a gas-phase chain terminator to elucidate the locations of the normal initiation and termination reactions. Experience indicates, however, that adding a new species to a reacting mixture frequently raises more questions than it answers. 

Copper-chromium catalysts employed for CO oxidation were found to be affected by composition and pretreatment parameters. CuCr20i, was more active than CuO only if prereduction was carried out and if metal concentration on alumina support was larger than 12 w t %. The presence of Cr with Cu in the oxide limited the extent of catalyst reduction leading also to less deactivation as compared to Cu on alumina. The presence of Cr also decreased an activity inhibition effected by water. A supported Cu-Cr catalyst used in an automobile ran with leaded petrol was deactivated by lead deposition. Deposits were mainly lead sulphate located on pellet periphery. Also, lead was preferentially distributed on the alumina instead of on the active metal-rich zones of the catalysts. 

The present communication reports results regarding CO oxidation over copper-chromium catalysts. The work was started studying unsupported catalysts and then supporting on alumina, looking for optima catalyst composition and pretreatment. Afterwards, the... 

The first part of this work was devoted to an optimization study of the composition and pretreatment parameters of unsupported and supported copper and copper-chromium catalysts for the reaction of oxidation of CO. 

In view of the uncertainties inherent in Hammett indicator determinations of surface acidity by visual means, a study was made of the spectral behavior of dyes adsorbed on several silica-alumina catalysts and silica gel (62). The effects of catalyst water content, dye concentration, catalyst composition and pretreatment on the spectra of the adsorbed dyes were examined. The Hammett indicator dyes employed and their corresponding pKA values are summarized in Table II. Reference spectra were determined for the base-form of the dye in iso-octane or methylene chloride solution and for the acid-form in an aqueous sulfuric acid or ethanolic-hydrogen chloride solution. Dyes were adsorbed from isooctane solutions onto thin plates of optically transparent catalysts which were installed in evacuated cells of design similar to that shown in Fig. 4. The catalysts samples were routinely pretreated by calcination in oxygen at 500° to remove any organic contaminants, followed by evacuation at this temperature. To examine the effect of variable water content on the spectra the samples were rehydrated in an atmosphere of wateir vapor for 24 hr after pretreatment and subsequently evacuated at some lower temperature. Dye solutions were introduced through a side arm. These solutions were suitably dilute so that the absorbance due to dissolved dye was either below the limits of detection or, at... 

Cu-chromite catalysts CO in air H O added in some runs 200 - 400 1 atm NR Study of catalyst composition and pretreatment effects on CO oxidation 107... 

Haber and Klemensiewicz also made an important contribution to the knowledge of the effect of glass composition and pretreatment on glass electrode response. 

Membrane replacement cost can be considered as operational cost as well. Up to now, there is little rehable information on the lifetime of membranes. Although some membrane systems have been in operation for 6 years without failure or with an annual replacement rate of less than 3% (Churchhouse and Brindle, 2002), others had to be replaced after 2-3 years because of serious fouhng, braiding, sludging, or even meehanieal destruction. It is evident that lifetime is correlated with the composition and pretreatment of the waste-water, the applied cleaning strategies, as well as with the type of membrane and module construction. 

Pretreating the feedstocks with hydrogen is not always effective in reducing heavy metals, and it is expensive. Other means that proved successful are modifying the composition and the microporous structure of the catalyst or adding metals like Sb, Bi or Sn, or Sb-Sn combination. Antimony organics have been shown to reduce by 50% gas formation due to metal contaminants, especially nickel. ... 

The catalytic activity of an electrode is determined not only by the natnre of the electrode metal (its bulk properties) but also by the composition and stmcture of the snr-face on which the electrochemical reaction takes place. These parameters, in tnm, depend on factors such as the method of electrode preparation, the methods of snr-face pretreatment, conditions of storage, and others, all having little effect on the bulk properties. 

A new HP-TLC method has been applied for the quantitative analysis of flavonoids in Passiflora coerulea L. The objective of the experiments was the separation and identification of the compound(s) responsible for the anxiolytic effect of the plant. Samples were extracted with 60 per cent ethanol or refluxed three times with aqueous methanol, and the supernatants were employed for HPTLC analysis. Separation was performed on a silica layer prewashed with methanol and pretreated with 0.1 M K2HP04, the optimal mobile phase composition being ethyl acetate-formic acid-water (9 1 l,v/v). It was established that the best extraction efficacy can be achieved with 60 - 80 per cent aqueous methanol. The HPTLC technique separates 10 different flavonoids, which can be used for the authenticity test of this medicinal plant [121],... 

Phosphorus is manufactured by the reduction of commercial-quality phosphate rock by coke in an electric furnace, with silica used as a flux. Slag, ferrophosphorus (from iron contained in the phosphate rock), and carbon monoxide are reaction byproducts. The standard process, as shown in Figure 2, consists of three basic parts phosphate rock preparation, smelting in an electric furnace, and recovery of the resulting phosphoms. Phosphate rock ores are first blended so that the furnace feed is of uniform composition and then pretreated by heat drying, sizing or agglomerating the particles, and heat treatment. 

Substrate and Pretreatment. Sweet corn (hybrid Lingodor) of W.H. Perron Laval, Quebec was grown in well prepared soil in a plot of 3 x 2 meters. Corn stalks were ground to 20 mesh to be used as a substrate. It was pretreated with 1.5% sodium hydroxide (NaOH) wt/vol with substraterwater ratio of 1 10 at 121 C for 60 minutes. The substrate was not washed after the pretreatment, and all the solubilized polymers (hemicelluloses and lignin) were retained along with the insoluble polymer (cellulose) in the fermentation medium. The composition of corn stalk is presented in Table 1. 

Catalyst preparation is crucial in successful Fischer-Tropsch synthesis. Appropriate catalyst composition and delicate pretreatment and operating conditions are all necessary preconditions to achieve the desired results. Catalyst disintegration brought about by oxidation and carbide formation is a serious problem that can be prevented only by using catalysts with adequate chemical and mechanical stability under appropriate operating conditions. 

The oxidation of carbon monoxide on nickel oxide has often been investigated (4, 6, 8, 9, II, 16, 17, 21, 22, 26, 27, 29, 32, 33, 36) with attempts to correlate the changes in the apparent activation energy with the modification of the electronic structure of the catalyst. Published results are not in agreement (6,11,21,22,26,27,32,33). Some discrepancies would be caused by the different temperature ranges used (27). However, the preparation and the pretreatments of nickel oxide were, in many cases, different, and consequently the surface structure of the catalysts—i.e., their composition and the nature and concentration of surface defects— were probably different. Therefore, an explanation of the disagreement may be that the surface structure of the semiconducting catalyst (and not only its surface or bulk electronic properties) influences its activity. 

If the objective is a pragmatic study of the effects of variables such as composition, preparation, and pretreatment on the acidic properties of a solid catalyst, the catalytic titration method would be the most relevant way to determine number and strength of the acid sites that form the seat of catalytic activity. Further understanding could then be gained by complementing the catalytic method with an independent study using a tool such as infrared spectroscopy. 

These compositional considerations necessitate attention to raw materials evaluation early in process research and development to (1) establish an in-depth knowledge of the principal raw material, including its composition and history of materials handling prior to arrival at the factory, (2) investigate the effects of seasonal variations and storage under various conditions on composition and on hydrolytic performance, and (3) explore alternative pretreatment processes for upgrading the composition and hydrolytic performance of available raw materials. The resource that is for sale is not pure cellulose it is a complex mixture containing cellulose caveat emptor. 

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