(522e) DFT and Microkinetic Modeling Study of Ethanol from Syngas on Co7Pd6 Nanocluster

Global energy demand is increasing continuously with the rising urbanization, industrialization, and with raise in personal and transportation needs. Most of the world transportation relies on liquid fuels, to meet the ever growing demand there is a need to increase the production of liquid fuels. Ethanol is considered as an alternative liquid fuel. In the current project we are interested to study ethanol production from Syngas. Syngas is a mixture of CO and H₂. Syngas is an important feedstock for many chemical processes, it can be produced from Methane by steam reforming or partial oxidation processes.

Syngas to ethanol process has been studied previously and the most favorable catalyst element is rhodium. Because of the low cost and less availability of rhodium there is a search for alternatives. In the current study we propose a bimetallic catalyst. Ethanol formation from syngas is a two-step process which involves chain growth and alcohol formation. The two metals in our bimetallic catalysts are chosen such that, one aids in chain growth (Co) and other aids in alcohol formation step (Pd).

In this study, we used a bimetallic 13 atom Nano catalyst consisting of seven cobalt and six palladium atoms (Co₇Pd₆), to understand the reaction mechanism. Our reaction mechanism includes 37 reactions involving 21 intermediates, 2 reactants (CO and H₂) and 5 products (ethanol, methane, methanol, acetaldehyde and water).

DFT studies are performed using Jaguar 7.0, an atomic orbital method and adsorption energies of all intermediate species is determined, transition state energies are determined for key reactions using NEB methods, BEP relationship is determined to reduce the computational cost, activation energies, heat of reactions and entropy are calculated together with DFT simulations and BEP relationship. To define the exact exchange energy B3LYP a hybrid functional is used and LACVP is used to define the molecular orbitals. All energy calculations are spin polarized and zero point energy corrected.

To quantify the amount of products formed and concentration of intermediates on the surface a Microkinetic model is developed in Matlab. A batch reactor is designed, seven ODE’s for reactant consumption and production formation together with 21 ODE’s which represent the change in concentration of intermediates are solved simultaneously using Matlab’s inbuilt ODE solver. Consumption of reactants, change in concentration of surface species and evolution of products with time are determined.

Our results compare well with literature (experimental and other theoretical results) for adsorption energies and vibrational frequencies. Our microkinetic model to an extent incorporates coverage effects of CO on all the three cobalt, palladium and cobalt palladium surfaces.