Direct synthesis of Pd incorporated in mesoporous silica for solvent-free selective hydrogenation of chloronitrobenzenes

- Pd incorporated in mesoporous silica (Pd-MS) catalysts were prepared via direct synthesis method.
- The formation mechanism of Pd-MS catalysts with 1, 3, 5-trimethylbenzene (TMB) was proposed.
- The catalytic activity of Pd-MS-x-TMB increased with increasing pH value (x meant x/10 mL NH3·H2O).
- The selectivity to p-CAN was 99.9% at 100% p-CNB conversion by Pd-MS-50-TMB at 85 °C, 3.45 MPa and 2 h.
- Pd-MS-50-TMB was also found to be effective for solvent-free hydrogenation of m-CNB and o-CNB.

Pd incorporated in mesoporous silica (Pd-MS) catalysts were prepared by a direct synthesis method in the presence of 1, 3, 5-trimethylbenzene (TMB) and their formation mechanism was proposed. TMB not only acted as an effective expanding agent to enlarge pore size and pore volume of MS but also acted as a structure-directing agent to induce the formation of worm-like morphology. For solvent-free hydrogenation of p-chloronitrobenzene (p-CNB), a complete conversion of p-CNB with a selectivity towards p-chloroaniline of 99.9% over the Pd-MS catalyst with addition of TMB (Pd-MS-50-TMB, where 50 represented the addition of 5 mL of aqueous NH3) was obtained at 85 °C and 3.45 MPa of H2 in 2 h, while only 48.4% p-CNB conversion over Pd-MS-50 synthesized without TMB was obtained. The enhanced activity of the Pd-MS-50-TMB was not only attributed to the smaller size of Pd particles, but also to the worm-like morphology of the support with larger pore size and pore volume that could enhance mass transfer and allow the reactants more facile access to Pd for reaction.

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