Sequencing of pretreatment

Although sequencing of pretreatment technologies is always site specific, there are some generalizations that can be made. Figure 8.21... 

Although sequencing of pretreatment technologies is always site specific, there are some generalizations that can be made. Figure 8.21 shows a typical process flow diagram that includes many of the pre- treatment technologies described above. Note that most RO systems will not include all of these unit operations. 

Similarly, it is apparent that chlorpromazine does not prevent the LSD sequence of effects and, when given during the LSD experience, may mask perception of some of the changes but not the course of the march of events. Indeed, because of the effects of chlorpromazine per se, most clinicians treating bad trips have learned, if medications are to be used, to employ sedative antianxiety drugs, such as valium. Animal experiments tell us that remarkably small doses of chlorpromazine can be strikingly effective in blocking the effects of LSD on fixed ratio performance (30 Mg/kg), and there was some early hint that less of a 5-HT elevation occurred with chlorpromazine pretreatment in rat brain (22). 

Activation (of noble metal electrodes) — Noble metal electrodes never work well without appropriate pretreatment. Polycrystalline electrodes are polished with diamond or alumina particles of size from 10 pm to a fraction of 1 pm to obtain the mirror-like surface. The suspensions of polishing microparticles are available in aqueous and oil media. The medium employed determines the final hydrophobicity of the electrode. The mechanical treatment is often followed by electrochemical cleaning. There is no common electrochemical procedure and hundreds of papers on the electrochemical activation of -> gold and platinum (- electrode materials) aimed at a particular problem have been published in the literature. Most often, -> cyclic and - square-wave voltammetry and a sequence of potential - pulses are used. For platinum electrodes, it is important that during this prepolarization step the electrode is covered consecutively by a layer of platinum oxide and a layer of adsorbed hydrogen. In the work with single-crystal (- monocrystal) electrodes the preliminary polishing of the surface can not be done. 

Even for a single system, the conditions may be such that the history of the sample can have an effect. Spillover involves a sequence of steps and each of these steps may be influenced by the pretreatment of the sample. As an example, surface transport and surface activation may depend on hydroxyl content (via Hsp + OH -> OH + H p and Hsp + MOH ->M + HzO mechanisms, respectively). Dehydroxylation of an oxide surface may, therefore, reduce the rate and extent of Hsp transport or subsequent surface activation (137). 

The sequence of TPR profiles for the Rh/Al 0 catalyst after different pretreatments are shown in Fig. lb A clear difference is observed In the first oxidation (400 C) - reduction cycle (denoted as 1-ox-400), relative to the subsequent cycles. In the first cycle, the consumption was significantly lower and extended to higher reduction temperatures. 

In this work the hydrogenolysis of ethyl laurate (EL) to dodecanol (ROH) and ethanol has been studied on different Ru-Sn/ALOs catalysts. Systematic studies have been made to investigate the influence of precursor compounds, sequence of impregnation, metal loading, Sn Ru atomic ratio, catalyst pretreatment (calcination, reduction) and reaction conditions (temperature, H2 pressure). The calcined catalysts were characterized by Ten erature Programmed Reduction (TPR). Correlation between the activity and TPR characteristics of Ru-Sn/Al203 catalysts was also demonstrated. 

---