Boron Switch for Selectivity of Catalytic Dehydrogenation on Size-Selected Pt Clusters on Al₂O₃

Abstract

Size--selected supported clusters of transition metals can be remarkable and highly tunable catalysts. A par--ticular example is Pt clusters deposited on alumina, which have been shown to dehydrogenate hydrocarbons in a size--specific manner. 1 Pt 7 , of the three sizes studied, is the most active and therefore like many other catalysts, deactivates by coking during reactions in hydrocarbon--rich environments. Using a combination of experiment and theory, we show that nano--alloying Pt 7 with boron modifies the alkene--binding affinity to reduce coking. From a fundamental perspective, the comparison of experimental and theoretical results shows the importance of considering not simply the most stable clus--ter isomer, but rather the ensemble of accessible structures as it changes in response to temperature and reagent cover--age.

Oxidative Dehydrogenation of Cyclohexane by Cu vs Pd Clusters: Selectivity Control by Specific Cluster Dynamics

“…However, in one exhaustive study we showed that at least for Pt clusters on α‐alumina, the cluster isomerization is highly facile, and all of ∼30 low‐energy minima are indeed easily visited by the system in under 1 ns . Furthermore, since we introduced the Boltzmann ensemble approach, we successfully used it to describe a number of cluster catalyst properties, such as sintering on the support, size‐specific catalytic activity, and composition‐dependent selectivity, in agreement with experiment when it was available . In the case of Pd on UNCD, we note that the global minimum may constitute only circa 43–46 % of the population, depending on the reaction step (see Figure , ∼43 % for global minimum of adsorbed C 6 H 12 ; ∼46 % for adsorbed C 6 H 10 ).…”

“…Therefore, the global minimum alone cannot accurately represent the catalyst. Less stable isomers are likely to be more chemically reactive and therefore cannot be ignored . In Table , we specify the number of thermally‐relevant isomers of supported clusters and the average charges on the metal atoms.…”

Surface‐supported cluster catalysis: Ensembles of metastable states run the show

“…Next, following our theoretical proposal that dehydrogenation can be made more selective by adding some boron to Pt, experiment was done and confirmed the effect . In calculations, the global minimum of Pt 7 B on Al 2 O 3 has in fact greater affinity to carbon than does the pure Pt 7 on Al 2 O 3 .…”

Atomistic Models for Highly‐Dispersed PtSn/γ‐Al2O3 Catalysts: Ductility and Dilution Affect the Affinity for Hydrogen

“…Significant amount of work has been devoted so far for the proposal of relevant dispersed monometallic Pt/Al 2 O 3 models, particularly in the case of the gamma polymorph of alumina . The ductility of small platinum clusters (typically, Pt 13 ) appears to be very strong, in the presence of hydrogen, oxygen and hydrocarbons despite the interaction with a support. Moreover, it was shown that Pt 13 clusters exhibit a higher adsorption capacity than the infinite Pt(111) surface .…”