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.
Yucong Song,Xiaoshu Ding,Fang Li,Dongsheng Zhang,Xinqiang Zhao,Yanji Wang
Methylcyclohexane diisocyanate (HTDI) is the core raw material for the synthesis of high-grade polyurethane . Aiming at the problems existing environmental pollution and safety risks in the phosgene process, a novel and green synthesis route of HTDI was proposed. We studied the catalytic hydrogenation of dimethyl toluene dicarbamate (TDC) benzene ring to methyl cyclohexyldicarbamate (HTDC) in this novel route. The effects of metal active components, supports and metal Rh loadings on the catalytic performance were investigated. It was found that the supported Rh/γ-Al 2 O 3 catalyst had excellent catalytic activity and selectivity. The yield of HTDC was close to 100 % at 100 °C under 3 MPa hydrogen pressure. However, the catalyst was deactivated seriously after the reaction. The organic matter adsorbed on the catalyst surface and covered the active metal was the main reason for the catalyst deactivation . Fortunately, the deactivated catalyst could be regenerated by solvent washing and high temperature calcination .
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