Promoters and Poisons

Wimmer E, Fu C L and Freeman A J 1985 Catalytic promotion and poisoning all-electron local-density-functional theory of CO on Ni(001) surfaces coadsorbed with K or S Phys. Rev. Lett. 55 2618-21... 

In section 2.5 we have examined the effect of promoters and poisons on the chemisorption of some key reactants on catalyst surfaces.We saw that despite the individual geometric and electronic complexities of each system there are some simple rules, presented at the beginning of section 2.5 which are always obeyed. These rules enable us to make some predictions on the effect of electropositive or electronegative promoters on the coverage of catalytic reactants during a catalytic reaction. 

Thus the promoting and poisoning role of Li, or any other alkali, can be predicted in a qualitative way from the simple rules of section 2.5 or, equivalently, from equations (2.28) and (2.29). 

Knowledge of the stracture and bonding of molecnles to snrfaces has been obtained from such techniques as LEED, electron energy-loss spectroscopy (EELS), secondaiy-ion mass spectrometry (SIMS), infrared spectroscopy (IRS), Raman spectroscopy, and NMR spectrometiy. The scope of snch studies needs to be greatly expanded to include the effects of coadsorbates, promoters, and poisons. Greater emphasis should be given to developing new photon spectroscopies that would permit observation of adsorbed species in the presence of a gas... 

Recent theoretical studies have demonstrated that it is possible to calculate accurately adsorbate stmcture and energy levels, to explain trends with variations in metal composition, and to interpret and predict the influence of promoters and poisons on the adsorption of reactants. Additional efforts along these lines will contribute greatly to understanding how catalyst stmcture and composition influence catalyst-adsorbate interactions and the reactions of adsorbed species on a catalyst surface. With sufficient development of theoretical methods, it should be possible to predict the desired catalyst composition and stmcture to catalyze specific reactions prior to formulation and testing of new catalysts. 

Analytical electron microscopy permits structural and chemical analyses of catalyst areas nearly 1000 times smaller than those studied by conventional bulk analysis techniques. Quantitative x-ray analyses of bismuth molybdates are shown from lOnm diameter regions to better than 5% relative accuracy for the elements 61 and Mo. Digital x-ray images show qualitative 2-dimensional distributions of elements with a lateral spatial resolution of lOnm in supported Pd catalysts and ZSM-5 zeolites. Fine structure in CuLj 2 edges from electron energy loss spectroscopy indicate d>ether the copper is in the form of Cu metal or Cu oxide. These techniques should prove to be of great utility for the analysis of active phases, promoters, and poisons. 

Broqvist, P., Molina, L.M., Gronbecka, H. and Hammer, B. (2004) Promoting and poisoning effects of Na and Cl coadsorption on CO oxidation over MgO-supported Au nanopartides. Journal of Catalysis, 227, 217-226. 

Kizhakevariam N, Stuve EM. 1993. Promotion and poisoning of the reaction of methanol on clean and modified platinum (100). Surf Sci 286 246-260. 

Equations (31) and (29) explain the mechanism of the promoter and poisoning action of impurities. An impurity is a... 

We see that the promoter and poisoning action of an impurity are determined not only and not so much by the nature of the impurity and the character of the reaction as by the position of the Fermi level on the surface of the crystal, i.e., by the state of the system as a whole. The condition (33a), which is valid at certain values of T and Z, may be replaced by the... 

J.5. Effects of additives, promoters, and poisons on sintering behavior... 

Box 5 Coping with Iodide both as Promoter and Poison Making the Iridium Catalyzed Process Work Well... 

Thus, complex high-area catalysts are typically not the best for fundamental investigations at the atomic or molecular level. Although many broadly important characteristics of heterogeneous catalysis, such as metal particle size effects, support effects, metal—support interaction, and the influence of the promoters and poisons... 

D.A. King. D.P. Woodruff. The Chemical Physics of Solid Surfaces and Heterogeneous Catalysis, Elsevier (1981,. ..). (A series of the "Advances" type, many experimental results, less emphasis on techniques. Volume 1 (1981) deals with clean solid surfaces. Vol. 2 (1983) with adsorption at solid surfaces. Volume 6 (1993) with co-(chemi-)-sorption, promoters and poisons.)... 

Early higher pressure reaction smdies over Pt-Sn model catalysts by Paffett [62,63] and Somorjai [64, 65] and their coworkers revealed new insights into hydrocarbon catalysis in such systems. Szanyi et al. [62] showed that n-butane hydrogenolysis under moderate pressures (1-200 Torr H3/butane=20) and temperatures (up to 650 K) could be carried out without disruption of the ordered Sn/Pt(lll) surface alloys. This established that such catalytic reactions could be studied while maintaining the composition and geometric structure of these alloys under reducing reaction conditions (but not catalytic oxidation due to the aggressive interaction of O3 with Sn). These ordered Sn/Pt surfaces are qualitatively different from those in many studies of promoters and poisons, or disordered alloys, e.g., Au-Pt, in which the quantitative information on ensemble sizes available for reactions is difficult to determine. 

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