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.