Stability and C-H activation of the Periana PtCl2 Catalyst for activating methane to methanol
Jeremy Kua and William A. Goddard III*
Materials and Process Simulation Center, Beckman Institute (139-74), Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125
Using first principles quantum mechanics [nonlocal density functional theory (B3LYP), we have studied the relative stability of the Pt(NH3)2Cl2 and Pt(bpym)Cl2 complexes in concentrated sulfuric acid, involved in the high-yield catalytic conversion of methane to methylbisulfate reported by Periana et al. (Science, 1998, 280, 560). We have applied the Poisson-Boltzmann continuum to model solvation of these complexes. We find that the ammine complex is unstable in sulfuric acid and the active catalyst in this case has bisulfate ligands. The bisulfate catalyst is also found to favorably lead to precipitation of PtCl2 leading to catalyst death. The bipyrimidine catalyst on the other hand is stable in solution. We find that the bipyrimidine catalyst has a marginally lower barrier to C-H activation compared to the bisulfate catalyst. Thermodynamics suggest that the oxidation step is more favorable for the bisulfate catalyst. Bipyrmidine acts as a "proton sink" and thus allows the protonated form of the ligand to remain bound to Pt in concentrated sulfuric acid.
Funding: NSF, Chevron