(47e) Catalytic Carbonylation With Rh

Methanol carbonylation to acetic acid is an important commercialized process. However, there are comparatively very few reports on higher carbon number alcohol carbonylation and for supported catalysts. This talk will describe recent studies aimed at understanding carbonylation of higher alcohols primarily using Rh-based solid catalysts in either the vapor or condensed phases. This work addresses increasing interest in using novel feedstocks to synthesize important chemical intermediates.

Catalysts consisted of Rh loaded onto Na zeolites or alkali-exchanged heteropolyacids, as has been used in alcohol carbonylation. [1,2] Rh catalysts are well known for methanol carbonylation.[3] Gas phase reactions were carried out in atmospheric pressure plug flow microreactors with alcohol and iodide promoter delivered by liquid syringe pump and vaporized into the CO feed. Liquid phase reactions were carried out in 160 mL Parr reaction vessels with magnetic stirring and up to 60 bar CO. Relative ratios of alcohol, promoter, and CO partial pressures were varied, as were space velocities. Temperatures were held constant between 100°C – 250°C. Product concentrations were measured by GC-FID with good mass balance, excluding CO and CO2.

Significant results include the verification of apparent activation barriers from the literature (e.g. [1]) and identification of temperature windows for optimum product yields in both the vapor and condensed phases. Iodide promoters were seen to initiate the catalytic cycle, leading, for example, to propianoates or acetates depending on the nature of the promoter. Carboxylic acid yields were strongly driven by the residual acidity of the supports, with carbonylation rates decreasing and carboxylate selectivities sharply increasing with decreasing acidity, an effect seen previously.[2] Catalytic results are supported by physical (BET, ICP, ammonia TPD, etc) and spectroscopic (DRUV-vis, XPS, and XAS) characterization and give suggestions into the design of future materials.

[1] M.S. Scurrell, T. Hauberg, Appl. Catal. 2 (1982) 225.

[2] L.D. Dingwall, A.F. Lee, J.M. Lynam, K. Wilson, L. Olivi, J.M.S. Deeley, S. Gaemers, G.J. Sunley, ACS Catal. 2 (2012) 1368.

[3] J.F. Roth, J.H. Craddock, A. Hershman, F.E. Paulik, Chem. Tech. (1971) 600.