(78c) Rational Design of Bimetallic Syn-Gas to Ethanol Catalysts

A major challenge associated with the synthesis of ethanol from syn-gas is an inability to find a low-cost catalyst that promotes the proper combination of CO dissociation and CO insertion steps, so as to yield ethanol as the primary reaction product and inhibit the formation of methane, methanol, longer chain alkanes, and other coking reaction products. Given the complexity of this reaction system, a simple trial-and-error approach to catalyst design is fraught with difficulties, which could severely limit efforts to identify an ideal catalyst material.  Therefore, we used quantum mechanical simulations for the rational design of bimetallic catalysts that are optimally suited for the production of ethanol from syn-gas.  Specifically, Density Functional Theory (DFT) simulations and Bronsted-Evans-Polanyi (BEP) relations were used to map out the full reaction mechanism from syn-gas to ethanol for 16 different bimetallic clusters that range in size from 13 to 38 metal atoms. These efforts were accelerated by the identification of key reaction descriptors that enabled the elimination of bimetallic systems that were less likely to be effective catalysts for the desired reactions. For the more promising bimetallic catalysts, microkinetic models were built, considering all necessary adsorption and reaction steps as well as the diffusion of intermediate species between varying metal surface sites. These simulations indicate the nature and stability of the various bimetallic nanocatalysts and more importantly identify specific metal combinations that are ideally suited for ethanol production.  Select catalyst formulations were prepared and tested for catalytic activity and selectivity.  These experimental were used to validate the computational results.