452585 The Role of the Support for Pt Catalysts during the Water-Gas Shift Reaction

Friday, November 18, 2016: 9:10 AM
Franciscan D (Hilton San Francisco Union Square)
Viktor Cybulskis, Yanran Cui, Mayank Shekhar, Juan Lovón Quintana, W. Nicholas Delgass and Fabio H. Ribeiro, School of Chemical Engineering, Purdue University, West Lafayette, IN

The Role of the Support for Pt Catalysts during the Water-Gas Shift Reaction

Viktor J. Cybulskis, Yanran Cui, Mayank Shekhar, Juan J. Lov—n Quintana, W. Nicholas Delgass, Fabio H. Ribeiro *

School of Chemical Engineering, Purdue University, West Lafayette, IN 47907

Because of its relative simplicity, the water-gas shift (WGS) reaction is an ideal system for studying catalytic chemistry on supported noble metal surfaces at the molecular level. There is a general consensus that the most active WGS catalysts are bi-functional in nature with contributions from both the dispersed metal and as well as the support in activating CO and H2O, respectively [1, 2]. On supported Pt catalysts, the WGS turnover frequency (TOF) per surface metal has been shown to be independent of the Pt particle size [3, 4], but can vary by a factor of 100 depending upon the reducibility of the support as shown in Figure 1. For this study, we combined operando infrared spectroscopy (IR) and transient kinetics with CO/13CO and H2O/D2O isotope switches to examine the carbon and hydrogen reactive pools on Pt/Al2O3, Pt/ZrO2, Pt/CeO2, and Na-Pt/Al2O3 while correlating catalyst performance with surface features related to CO and H2O activation.

The presence of a hydrogen/deuterium (H/D) kinetic isotope effect (KIE) along with time-resolved IR spectra of transient surface species, reveals that O-H bond breaking is involved in the rate-determining step on alkali-free Pt catalysts. The addition of Na to these Pt-containing materials leads to the formation of new H2O activation sites that modify the rate-determining O-H dissociation step such that nearly all of the CO adsorbed on the Pt surface is able to participate in the reaction. The implications of these findings on the elementary kinetic steps for WGS, the number of true catalytic sites, and the variation in WGS TOF on supported Pt catalysts will be discussed.

Figure 1. Comparison of WGS TOF per surface Pt at 300 ¡C (22% H2O, 7% CO, 37% H2, 9% CO2) for various supports.

REFERENCES

[1]   C. M. Kalamaras, P. Panagiotopoulou, D. I. Kondarides, and A. M. Efstathiou, J. Catal. 264 (2009) 117.

[2]   G. Jacobs, P. M. Patterson, U. M. Graham, D. E. Sparks, and B. H. Davis, Appl. Catal. A: Gen. 269 (2004) 63.

[3]   P. Panagiotopoulou, and D. I. Kondarides, Catal. Today 112 (2006) 49.

[4]   M. Shekhar, J. Wang, W.-S. Lee, W. D. Williams, S.M. Kim, E. A. Stach, J. T. Miller, W. N. Delgass, and F. H. Ribeiro, J. Am. Chem. Soc. 134 (2012) 4700.


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