Catalysts catalyst pretreatment, effects

Figure 4 Effect of repeated reaction cycles and catalyst pretreatment in 6.2 M NaOH at 473 K on rate constant and catalyst surface area for ethanolamine dehydrogenation over unpromoted skeletal copper under standard conditions.

Effect of Metal Oxide Additives on Au/Ti02, Catalyst Pretreated 200°C CaO, ZnO... 

The deoitygenation reaction of ethyl stearate was carried out for 4-6 h at reaction temperatures between 270-360°C and under reactor pressure of 0-7 bar. The effect of the catalyst pretreatment and the catalyst mass as well as the influence of reaction temperature were studied. The observed products in the ethyl stearate reaction are the deoxygenation products (desired), intermediate product (fatty acid), hydrogenation products (unsaturated Et-SA) and by-products (Figure 3). 

Surface effects and adsorption equilibria thus will significantly influence the course of photoelectrochemical transformations since they will effectively control the movement of reagents from the electrolyte to the photoactivated surface as well as the desorption of products (avoiding overreaction or complete mineralization). The stability and accessibility toward intermolecular reaction of photogenerated intermediates will also be controlled by the photocatalyst surface. Since diffusion and mass transfer to and from the photocatalyst surface will also depend on the solvent and catalyst pretreatment, detailed quantitative descriptions will be difficult to transfer from one experiment to another, although qualitative principles governing these events can be easily recognized. 

Catalyst pretreatment. Already in the first reports by Orito et al. [31], the beneficial effects of preheating the catalyst in hydrogen at 300-400 °C, followed by soaking in a solution of the modifier were described. Later, it was found that the H2 treatment is crucial for Pt/Al203 catalysts... 

In view of the nature of the catalyst, the pretreatment, the reaction temperature range, the very large specific conversion rate, and the positive temperature coefficient it may be concluded that the reaction studied by Justi and Vieth was not the nondissociative conversion. Furthermore, Schwab and Kaiser (29) reported that they had been unable to confirm the Justi and Vieth results (over nickel wire). The writer (30) found no field effect for the conversion at 298 K greater than 0.5% over pretreated nickel wire up to 4 kOe. It is necessary to conclude that the Justi and Vieth work is of no significance insofar as the present paper is concerned, and also that there is doubt concerning the reality of their results. 

In analyzing the problem of the structure sensitivity of a reaction catalyzed by Pd catalysts, it is convenient to classify the reactions in terms of the temperature range in which the reactions proceed and/or in which Pd catalysts were pretreated in H2. The effects of reaction (pretreatment) temperature and the presence of hydrogen in a reaction system should be treated as follows ... 

Activity measurement 1,3 butadiene hydrogenation was chosen as a probe reaction. The four major products of 1,3 butadiene hydrogenation, namely 1-butene, n-butane, cis- and trans-2-butene were monitored to study the pretreatment effect on the selectivity. Activity measurements were conducted after preheating the catalysts in-situ in various atmospheres without exposure to air. Two pieces of film catalysts were placed in a 0.8 cm ID quartz tube reactor and were pretreated as follows. 

The second pretreatment was selected to study the effect of poisoning on the microstructure and activity. In this case, the catalysts were pretreated at 450°C in mixtures of H2S/H2 containing concentration (250 ppm and 3000 ppm) of H2S for 8hrs. The catalyst was then reacted for 4 hrs in the same conditions as during activation without H2S present in the reaction mixture. 

It was found by Nis XPS studies of pyridine-adsorbed samples that after deactivation the surface acidic function changes in a different manner with the bulk acidity measured by infrared characteristic absorption bands of pyridine adsorbed samples [7], which would suggest different distributions of the acidic properties in the sample catalysts. The effects of additive elements on the overall acidic features of modified zeolite catalysts are dependent on sample pretreatment and/or reaction condition, which will contribute differently to the induced acidity on the surface and in bulk bifunctional properties, as examined by the reaction of n-heptane shown in Figure 1. 

The main aim of the present work has been to study the effects of the direct factors (which determine the coking rate in steam reforming) on the length of the induction period of coking and various ways of catalyst pretreatment (without or with the initiation of coking at a relatively high partial pressure of hydrocarbon) on the steady-state rate of coking,... 

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