(167b) Neopentane Hydrogenolysis Over Supported Pd and Pt Catalysts and Alloys: A Kinetics Study of Particle Size and Alloy Effects

Neopentane Hydrogenolysis over
Supported Pd and Pt
Catalysts and Alloys: A Kinetics Study of Particle Size and Alloy Effects

David J. Childers¹, Neil
Schweitzer², Arindom Saha³,
Robert M. Rioux³, Jeffery T. Miller² and Randall J. Meyer¹

¹University of Illinois at Chicago, Chicago, Illinois
60607 (USA)

²Argonne National Laboratory, Lemont, Illinois 60439
(USA)

3Pennsylvania State
University, University Park, PA 16802 (USA) 

The
demand for fossil fuels is continuing to grow despite the increasing emphasis
on finding replacement fuel sources. Therefore, advances in reforming processes
will be an important area for the foreseeable future. Selective isomerization
of high n-alkanes to branched hydrocarbons is one method to improve to quality
of these fuel stocks. There are competing pathways so selectivity is a very
important consideration. Bimetallic catalysts have become a significant point
in catalysis research in the past few decades [1]. Alloying has resulted in
increased activity and selectivity for various reactions, as well as improving
resistance to poisoning and sintering [1].

Both
Pt and Pd monometallic
catalysts had increased isomerization selectivity with increasing particle
size.  Pt and Pd catalysts displayed similar behavior for both
metals.  This trend for Pt has previously been observed by Foger
et al [2]. This change in selectivity could be explained two different ways:
ensemble effects and electronic effects. If a reaction requires more than one
active site to proceed then a change in the number of ensemble sites could be
the cause for the change in selectivity. Electronic effects on the other hand
are the changes in the electronic properties of the metal.  Metal atoms in different surface
configurations and particle sizes have different energetics which can affect
bond energies. Both these effects appear to be contributing to the change in
isomerization selectivity. First we find that the isomerization selectivity
appears to correlate well with CO adsorption strength: the weaker the adsorption
of CO, the higher the selectivity to isomerization.  In addition, alloying Pt
and Pd together has shown an increase in selectivity
compared to the single metal catalysts.  In
contrast, alloying Pd with Au has shown little change
in the selectivity.

References

1.     
J.H. Sinfelt, Sci.Am. 253 (1985)
90-&

2.     
K. Foger, and J.R. Anderson, Journal of Catalysis 54 (1978)
318-335.