Novel Dual-Bed Reactors:  Utilization of Hydrogen Spillover in Reactor Design

Abstract

Hydrogen spillover over macroscopic distances was demonstrated and exploited in the design of two novel catalytic reactors for 1-butene isomerization. A dual-bed reactor containing separate zones of noble metal and bimetallic catalysts yielded activities up to 2.7 times greater than that of the noble metal alone. The noble metal catalyst contained palladium supported on graphitic carbon. The bimetallic catalyst contained a base metal, either iron or cobalt, and a lanthanide metal, either cerium or praseodymium, also supported on graphitic carbon. The bimetallic catalysts by themselves had no measurable activity at the current experimental conditions. Results from a dual-bed, dual-feed reactor using the same catalysts showed dramatic activity increases relative to controls. In this reactor, the hydrocarbon never contacted the noble metal catalyst, yet substantial hydrocarbon conversion was measured. No hydrocarbon conversion was detected when blank support replaced the bimetallic catalyst or when no material at all was placed above the noble metal catalyst. In both reactors, the activity increase was attributed to hydrogen spillover. That is, molecular hydrogen adsorbed and dissociated on the noble metal catalyst. The adsorbed atomic hydrogen was then transported via surface diffusion to the bimetallic catalyst, activating those sites. The results also demonstrated that a catalytic reaction may occur at distinctly different reactive sites and that catalysts may be selected to promote specific steps within the reaction.

Modeling hydrogen spillover in dual‐bed catalytic reactors

“…Perhaps the most dramatic examples of this were given recently by Weigle and Phillips (2004), when they showed that hydrogen can diffuse to surfaces several centimeters from the source of the atomic hydrogen. This observation raises the question of how the phenomenon can be exploited in reactor design.…”

“…This fact is significant because the bimetallic catalyst alone shows no hydrocarbon conversion at the temperatures employed. Furthermore, Weigle and Phillips (2004) demonstrated that the activity increase is maintained when the two catalysts are present as distinct zones within the reactor. In fact, the reactants can be fed such that 1-butene only contacts the bimetallic catalyst, yet substantial hydrocarbon conversion is measured.…”

“…Numerous authors have demonstrated hydrogen spillover in systems where the hydrogen-generating surface is separated from a second type of active site (Weigle and Phillips, 2004;Chang et al, 1996;Chang and Phillips, 1997;Delmon, 1993;Baumgarten and Niemeyer, 2000;Baumgarten and Meyer, 2000a,b;Baumgarten and Maschke, 2000;Najafabadi et al, 2002;Roessner and Roland, 1996). Perhaps the most dramatic examples of this were given recently by Weigle and Phillips (2004), when they showed that hydrogen can diffuse to surfaces several centimeters from the source of the atomic hydrogen.…”

“…Recent work, however, demonstrates that combinations of catalysts can improve reactor performance, in terms of activity, selectivity, and deactivation (Chang, 1996(Chang, , 1997Weigle and Phillips, 2004;Delmon, 1993;Baumgarten and Meyer, 2000a). Phillips and coworkers described such a catalyst system for the isomerization of 1-butene to 2-butene (Chang, 1996(Chang, , 1997.…”

“…Each model describes the selective isomerization of 1-butene in a reactor of unique geometry. The reactors have been described in detail previously (Chang and Phillips, 1996;Weigle and Phillips (2004). Each model contains the same kinetic expressions, but differ with respect to the transport and boundary conditions.…”