Catalyst effect of temperature

Fig. 18. Conversion of n-hexane over CCU chlorinated platinum-alumina catalyst effect of temperature on reaction products 86). (Reprinted with permission of North-Holland Publishing Company.)...

Experiments both with homogeneous and heterogeneous catalyst. Effects of temperature and excess of alcohol in the initial mixture are studied. Non-negligible losses of the reactants in the permeate are observed. 

Sehested, J., Gelten, J. A. P., Remediakis, I. N., Bengaard, H., Nprskvo, J. K. (2004). Sintering of nickel steam-reforming catalysts effects of temperature and steam and hydrogen pressures. Journal of Catalysis, 223, 432—443. 

Gaur S, Pakhare D, Wu H, Haynes DJ, Spivey JJ (2012) CO2 reforming of CH4 over Ru-substituted pyrochlore catalysts effects of temperature and reactant feed ratio. Energy Fuels 26 1989-1998... 

Alma, M.H., Yoshioka, M., Yao, Y., and Shiraishi, N. (1996) Phenolation of Wood Using Oxalic Acid as a Catalyst Effect of Temperature and Hydrochloric Acid Addition, J. Appl. Polym. Sci. 61, 675-683. 

Reactor temperature and pressure. If there is a significant difierence between the effect of temperature or pressure on primary and byproduct reactions, then temperature and pressure should be manipulated to improve selectivity and minimize the waste generated by byproduct formation. d. Catalysts. Catalysts cam have a major influence on selectivity. Changing the catalyst can change the relative influence on the primary and byproduct reactions. 

These pioneers understood the interplay between chemical equiUbrium and reaction kinetics indeed, Haber s research, motivated by the development of a commercial process, helped to spur the development of the principles of physical chemistry that account for the effects of temperature and pressure on chemical equiUbrium and kinetics. The ammonia synthesis reaction is strongly equiUbrium limited. The equiUbrium conversion to ammonia is favored by high pressure and low temperature. Haber therefore recognized that the key to a successful process for making ammonia from hydrogen and nitrogen was a catalyst with a high activity to allow operation at low temperatures where the equiUbrium is relatively favorable. 

This is also an endothermic reaction, and the equilibrium production of aromatics is favored at higher temperatures and lower pressures. However, the relative rate of this reaction is much lower than the dehydrogenation of cyclohexanes. Table 3-6 shows the effect of temperature on the selectivity to benzene when reforming n-hexane using a platinum catalyst. 

This paper surveys the field of methanation from fundamentals through commercial application. Thermodynamic data are used to predict the effects of temperature, pressure, number of equilibrium reaction stages, and feed composition on methane yield. Mechanisms and proposed kinetic equations are reviewed. These equations cannot prove any one mechanism however, they give insight on relative catalyst activity and rate-controlling steps. Derivation of kinetic equations from the temperature profile in an adiabatic flow system is illustrated. Various catalysts and their preparation are discussed. Nickel seems best nickel catalysts apparently have active sites with AF 3 kcal which accounts for observed poisoning by sulfur and steam. Carbon laydown is thermodynamically possible in a methanator, but it can be avoided kinetically by proper catalyst selection. Proposed commercial methanation systems are reviewed. 

Findings with Bench-Scale Unit. We performed this type of process variable scan for several sets of catalyst-liquid pairs (e.g., Figure 2). In all cases, the data supported the proposed mechanism. Examination of the effect of temperature on the kinetic rate constant produced a typical Arrhenius plot (Figure 3). The activation energy calculated for all of the systems run in the bench-scale unit was 18,000-24,000 cal/g mole. 

Figure 4.12. Effect of temperature on the Tafel plots and corresponding I0 values of a Ag catalyst-YSZ interface during C2H4 oxidation on Ag.12 Reprinted with permission from Academic Press.

PETP flakes produced from used soft drinks bottles were subjected to alkaline hydrolysis in aqueous sodium hydroxide. A phase transfer catalyst (trioctylmethylammonium bromide) was used to enable the depolymerisation reaction to take place at room temperature and under mild conditions. The effects of temperature, alkali concentration, PETP particle size, PETP concentration and catalyst to PETP ratio on the reaction kinetics were studied. The disodium terephthalate produced was treated with sulphuric to give terephthalic acid of high purity. A simple theoretical model was developed to describe the hydrolysis rate. 17 refs. 

Fig. 2. Ihe effects of temperature on the conversions of CO2 and CH4 and the selectivity overNi-YSZ-Ce02 catalyst.

The effects of temperature on the conversions of CO2 and CH4 and the product distribution over Ni-YSZ-Ce02 catalyst are represented in Fig. 2. The concentrations of H2 and CO were slowly increased with increasing reaction temperature but those of CO2 and CH4 were decreased. Moreover, the concentrations of H2 and CO over Ni-YSZ-Ce02 catalyst were slightly higher than those over Ni-YSZ-MgO [7],... 

Fig. 1. Effects of temperature on the catalytic performance in the catalytic reforming of CFl by CO2 over Ni0-YSZ-Ce02 catalyst in a fixed bed reactor system.

Figure 3. Effect of temperature on the selectivity of the SCR reaction over CoZSM-5 (A) and HZSM-5 (B) catalysts. Feed contained 0.28% CH4, 0.21% NO and 2.6% O2 in He at a flow rate of 75 ml/min ( flow rates of CH4 and NO were 9.375 and 7.03//mol/min).

Figure 4.77 Effect of temperature and catalyst modularity on catalyst activity for ethylene polymerization [1].

Figure 6.15. Effect of temperature on stored NOx reduction in H2 (2000 ppm) balance He (total flow 200Ncc/min, catalyst weight 120 mg) over Pt—Ba/Al203 (1/20/100 w/w) catalyst at 200-300-400°C. H2, N2, H20 and NO are outlet concentrations, and H2 is inlet concentration.

Table 4 Hydrogenolysis of AcOBu on lRelPt(e,red.) catalyst in SPR16 reactor. Effect of temperature and concentration on conversion and reaction rate.

Figure 1 Effect of temperature on catalytic performance of Mg/Al/O catalyst in m-cresol methylation m-cresol conversion (u), selectivity to 3-MA (v), 2,3-DMP (X), 2,5-DMP (ct), 3,4-DMP (p), polyalkylates ( ).

The effect of temperature on the catalytic performance of Mg/Fe/O is reported in Figure 3. The behavior was quite different from that of the Mg/Al/O catalyst. The conversion of m-cresol with Mg/Fe/O was always lower than that with Mg/Al/O. The selectivity to 3-MA was almost negligible in the whole range of temperature. The selectivity to polyalkylates and to 3,4-DMP was also much lower than that observed with Mg/Al/O. Therefore, the catalyst was very selective to the products of ortho-C-methylation, 2,3-DMP and in particular 2,5-DMP. This behavior has to be attributed to specific surface features of Mg/Fe/O catalyst, that favor the ortho-C-methylation with respect to O-methylation. A different behavior of Mg/Al/O and Mg/Fe/O catalysts, having Mg/Me atomic ratio equal to 4, has also been recently reported by other authors for the reaction of phenol and o-cresol methylation [5], The effect was attributed to the different basic strength of catalysts. This explanation does not hold in our case, since a similar distribution of basic strength was obtained for Mg/Al/O and Mg/Fe/O catalysts [4],... 

Figure 3 Effect of temperature on catalytic performance of Mg/Fe/O catalyst in m-cresol methylation. Symbols as in Figure 1.

The Effect of Temperature The second parameter that we looked at was the effect of temperature. The temperature range studied was from 400°C to 700°C and tin (1% of the coal) as stannous chloride was used as the catalyst. 

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