The kinetics and mechanism of spillover

Levy, Ricardo B.; Boudart, M.

doi:10.1016/0021-9517(74)90080-3

Cited by 211 publications

(83 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Notably,a lthough the hydrogenation of catalyst supports can provide direct evidencef or hydrogen spillover, [3,[17][18][19][20][21] as in the case of Khoobiar's WO 3 reduction experiment, [3] its absence cannotd isprovet he presence of hydrogen spillover 'during catalysis'. From the catalytic viewpoint, hydrogen spillover can be used for varioush ydrogenation reactions if there is a' net migration' of Ha toms from the metal catalyst surface to the organic reactants.…”

Section: Understanding Hydrogen Spillover From a Catalysis Point Of Viewmentioning

confidence: 96%

Hydrogen Spillover in Encapsulated Metal Catalysts: New Opportunities for Designing Advanced Hydroprocessing Catalysts

2015

View full text Add to dashboard Cite

Hydrogen spillover has been one of the most debated concepts in the field of heterogeneous catalysis due to limited ways of studying it. The main controversies in hydrogen spillover, especially from the viewpoint of its catalytic functions, can be mainly attributed to the absence of well‐defined model catalysts that can provide direct proof of the catalytic functions of hydrogen spillover. In this article, we will provide an overview of the recent progress made with encapsulated metal catalysts, which can act as an ideal model catalyst for proving the existence and catalytic functions of hydrogen spillover. We will also demonstrate unique opportunities of using the encapsulated metal catalysts for designing advanced hydroprocessing catalysts with enhanced activity, distinct chemoselectivity, and increased catalyst durability.

show abstract

Section: Understanding Hydrogen Spillover From a Catalysis Point Of Viewmentioning

confidence: 96%

Hydrogen Spillover in Encapsulated Metal Catalysts: New Opportunities for Designing Advanced Hydroprocessing Catalysts

2015

View full text Add to dashboard Cite

show abstract

“…In at least one case, where surface transport is the slow step, it has been shown that the marked effect of adsorbed water on the rate of reaction is due to its influence on the rate of diffusion (Levy and Boudart, 1974). In this paper we report the effect of coadsorbed water on the surface diffusion of stearic acid on aluminum oxide.…”

Section: Scopementioning

confidence: 97%

“…Perhaps dual-functional catalysts can be made more effective by addition of a component to the reaction mixture which will increase the rate of transport between sites but not otherwise influence the catalysis. Water and alcohol have been shown to play such a role in the Pt catalyzed reduction of W 0 3 (Levy and Boudart, 1974).…”

Section: Conclusion and Significancementioning

confidence: 98%

Surface diffusion of stearic acid on aluminum oxide

1974

View full text Add to dashboard Cite

By means of infrared internal reflection spectroscopy we measured the time dependence of the surface concentration of stearic acid molecules over a well defined region of the surface. The molecules were diffusing into this region from a source comprising a compressed monolayer or bulk crystalline material outside the field of view. By these measurements in conjunction with solutions to the diffusion equations we determined the diffusion coefficient D, of stearic acid on the (0001) plane of a-alumina.We also determined the dependence of D, upon the amount of water CO-adsorbed on the surface. When the surface was free of reversibly adsorbed water, D, had a value of about 2 x 10-7 cm2/s. As the surface coverage of coadsorbed water increased to about a monolayer D, increased to a maximum value of about 4 x 10-5 cm2/s. With further additions of surface water D, then decreased and became less than 10-8 cm2/s at coverages slightly less than about two monolayers. In the region of its maximum value the temperature dependence of D, indicated SCOPEAn accurate experimental method is needed to measure surface diffusion rates on nonporous surfaces. Plane surfaces provide simple models for the study of the general phenomenon of surface flux which contributes to transport through catalyst pellets, adsorbent beds, and the diffusion barriers used in important separation processes. Most previous studies of surface diffusion have been based on a determination of total diffusive flow through porous materials. Gas chromatography, nuclear magnetic resonance, and neutron scattering spectroscopy have been employed for this purpose. The contribution due to Knudsen flow is then calculated and subtracted from the total. The difference is attributed to surface diffusion. Clearly, this approach is not applicable to nonvolatile species, but it is the least volatile component in any system which is most affected by surface diffusion.The direct measurements of surface diffusion on solids previously reported were by Beischer (1951) and Rideal and Tadayon (1954). They determined the diffusion coefficient of stearic acid on mica by means of radioactive tracer techniques. Our method is also based on a direct observation of transport in adsorbed layers on planar surfaces. It uses the somewhat simpler and more generally applicable technique of Internal Reflection Spectroscopy (IRS) to measure time dependent surface concentration. The results are combined with approximate solutions of the Fick diffusion equations under appropriate boundary conditions to give surface diffusion coefficients.Water adsorbed on a solid surface often has a dramatic effect upon the rates of interphase exchange or chemical reactions at that surface. In at least one case, where surface transport is the slow step, it has been shown that the marked effect of adsorbed water on the rate of reaction is due to its influence on the rate of diffusion (Levy and Boudart, 1974). In this paper we report the effect of coadsorbed water on the surface diffusion of stearic acid on aluminum ...

show abstract

“…The latter mechanism has received considerable attention in the literature for palladium, platinum, and nickel catalysts on oxide supports (Levy and Boudart, 1974;Sermon and Bond, 1973). To our knowledge, however, hydrogen spillover has not been studied with carbon-supported catalysts.…”

Section: Autoclave Reactormentioning

confidence: 98%