Bifunctional Organorhodium
Solid Acid Catalysts for
Methanol Carbonylation
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Abstract
Robust, bifunctional catalysts comprising Rh(CO)(Xantphos)
exchanged
phosphotungstic acids of general formulas [Rh(CO)(Xantphos)]<sup>+</sup><sub><i>n</i></sub>[H<sub>3–<i>n</i></sub>PW<sub>12</sub>O<sub>40</sub>]<sup><i>n</i>−</sup> have been synthesized over silica supports which exhibit tunable
activity and selectivity toward direct vapor phase methanol carbonylation.
The optimal Rh:acid ratio = 0.5, with higher rhodium concentrations
increasing the selectivity to methyl acetate over dimethyl ether at
the expense of lower acidity and poor activity. On-stream deactivation
above 200 °C reflects Rh decomplexation and reduction to Rh metal,
in conjunction with catalyst dehydration and loss of solid acidity
because of undesired methyl acetate hydrolysis, but can be alleviated
by water addition and lower temperature operation