Hydrocarbon Conversion Catalysis on Ceria-based Mixed Metal Oxides

Open Access
Author:
Mayernick, Adam David
Graduate Program:
Chemical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
January 14, 2011
Committee Members:
  • Michael John Janik, Dissertation Advisor
  • Michael John Janik, Committee Chair
  • Kristen Ann Fichthorn, Committee Member
  • Robert Martin Rioux Jr., Committee Member
  • Adrianus C Van Duin, Committee Member
Keywords:
  • Density Functional Theory
  • Palladium
  • Catalysis
  • Ceria
  • Hydrocarbon Oxidation
Abstract:
Ceria (CeO2) is a rare-earth metal oxide with a wide variety of applications in hydrocarbon conversion catalysis due to its ability to exchange lattice oxygen with reactant species. Ceria in combination with other rare earth or transition metals exhibits unique activity for hydrocarbon oxidation and high-temperature desulfurization. The structure and functionality of the transition metal-ceria surface is a function of synthesis and pretreatment methods, as well as catalytic operating conditions. The development of novel ceria-based catalysts is thus largely limited by difficulties in identifying the specific nature of active sites and establishing structure-function relationships therein. This dissertation utilizes computational chemistry methods to examine the catalytic stability and activity of transition metal-ceria surface structures at the atomistic level and motivate future efforts in catalyst design. Density functional theory and ab initio thermodynamics ares used to calculate activation barriers and free energies of elementary reaction steps. The activity and thermodynamic stability of supported Pd species on Pd-ceria oxidation catalysts are probed, with emphasis on quantifying the unique hydrocarbon oxidation activity of Pd-ceria mixed oxides. The C-H bond breaking activity of a series of transition metal-ceria mixed oxides is assessed, and a correlation is found between C-H activation energetics and oxide reducibility. The energetics of adsorption of H2S over ceria-lanthanide mixtures are also calculated, to assess the requirements of an effective ceria-based high temperature desulfurization sorbent. The use of DFT and reactive force field methods to probe multi-component heterogeneous catalyst surfaces is evaluated to direct future multi-scale studies of palladium-ceria oxidation catalysts and ceria-lanthanide desulfurization sorbents.