Scaling relationships between fundamental kinetic parameters for catalytic processes and descriptors of catalytic materials have greatly accelerated the use of computational methods such as DFT to screen and identify catalyst materials that are optimal for a given process. For example the barrier to a critical, rate-determining elementary step,△E‡¡ , can be correlated with electronic properties such as the d-band energy, Ed, thereby allowing Ed to be used, rather than △E‡¡, as the basis for rapid screening of new materials. We have developed the experimental analog to this methodological framework by using high throughput methods to make rapid parallel measurements of catalyst reaction kinetics and catalyst properties across continuous regions of alloy composition space. The kinetics of H2-D2 exchange have been measured at 100 compositions of the PdxAg1-x alloy with x = 0→1, in order to determine the barriers for dissociative adsorption and recombinative desorption of H2 as functions of alloy composition, △E‡ads (x) and △E‡des respectively. A number of catalyst properties have also been measured across alloy composition space: the d-band energy, Ed (x); surface segregation, θAg (x); and the hydrogen adsorption energy, △EH . Using alloy composition, x, as the parametric variable, these then allow the establishment of experiment-based scaling relationships such as △E‡ads (Ed). In the case of H2 adsorption these demonstrate the expected monotonic decrease of the △E‡ads with increasing Ed (relative to the Fermi level), but also reveal that the scaling is non-linear. This non-linearity may be a consequence of hydrogen-induced Pd segregation to the alloy surface.

Experimental establishment of scaling relationships for processes on alloy catalysts

2019 Spring National Meeting

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