Size effect of Rh/γ-Al2O3 catalyst in selective hydrogenation of dimethyl toluene-2,4-dicarbamate

The selective hydrogenation of dimethyl toluene-2,4-dicarbamate (TDC) to methyl cyclohexyl-2,4-dicarbamate (HTDC) is an important process for non-phosgene synthesis of methylcyclohexane-2,4-diisocyanate (HTDI). We prepared Rh/γ-Al 2 O 3 catalysts with an Rh particle size of 1.8–6.7 nm and studied size effect on TDC selective hydrogenation. The results showed that the catalytic activities of Rh/γ-Al 2 O 3 increase monotonously with increasing Rh particle size. This demonstrated that Rh/γ-Al 2 O 3 catalyst dedicates a negative size effect or an antipathetic structure sensitivity. Based on the characterization, we found that the geometric property of Rh is the main factor affecting the activity of catalyst. Combined with the proposed Rh particle model, it was inferred that the Rh (111) plays a major role in the TDC selective hydrogenation and the terrace sites are beneficial to promote the adsorption of TDC. The study on size effect can provide a guidance for the design and preparation of highly efficient Rh-based catalysts for TDC selective hydrogenation.