Influence of Pd deposition pH value on the performance of Pd-CuO/SiO₂ catalyst for semi-hydrogenation of 2-methyl-3-butyn-2-ol (MBY)

The selective hydrogenation of C[tbnd]C to C=C bonds is an important step, yet remains to be a great challenge in chemical industry. In this study, we have revealed the influence of Pd deposition pH value on the catalytic performance of Pd-CuO/SiO₂ catalyst for the semi-hydrogenation of 2-methyl-3-butyn-2-ol (MBY). Trace amount of Pd (about 500 ppm) was loaded via deposition-reduction method on CuO/SiO₂ support by using H₂PdCl₄ solution as precursor and NaBH₄ as reductant, respectively. The pH value at which Pd was deposited was adjusted to about 5 and 7 by adding NaOH solution. The obtained catalysts were characterized by several techniques including XRD, TEM, H₂-TPR, etc. In the case of pH value of 5, the CuO was partially dissolved during the deposition and then co-reduced with Pd²⁺ by NaBH₄, forming PdCu alloy structure in sub-nanometer. In contrast, no PdCu alloy structure was observed when pH value was 7. The kinetics of MBY semi-hydrogenation over both catalysts were compared. The former PdCu alloy catalyst showed very high selectivity towards the semi-hydrogenation of MBY due to its low activity in hydrogenation of C=C bond in 2-methyl-3-buten-2-ol (MBE). The results herein demonstrated that the pH value where Pd was deposited played a crucial role in determining the catalytic performance of PdCu catalyst.