Selective hydrogenation of 3-Hexyn-1-ol with Pd nanoparticles synthesized via microemulsions

- Pd nanoparticles of 4 to 8 nm size with a narrow size distribution were synthesized in a w/o microemulsion.
- Mesoporous FDU-12 silica with a 3D pore network was synthesized in the presence and absence of nanoparticles.
- Catalytic activity for the hydrogenation of 3-hexyn-1-ol with H2 was studied and compared to that of Lindlar and NanoSelectTM catalysts.
- New catalysts lead to high X and S for the Z-alkenol due to sintering of Pd particles and the removal of unselective edge Atoms.

In the study at hand we present a design strategy for novel catalysts which can be used for the selective hydrogenation of alkynes to alkenes. The design of the novel catalysts is based on two main ideas, namely (1) the synthesis of Pd nanoparticles via microemulsions and (2) the use of highly-ordered mesoporous silica with a 3-D pore network (FDU-12) serving as support. The nanoparticles are deposited on FDU-12 in two different ways. Firstly, we simply impregnated the support with a dispersion of the nanoparticles. The resulting catalyst was not selective at all; on the contrary, it fully hydrogenated our model alkyne, namely 3-hexyn-1-ol. Secondly, we synthesized the FDU-12 in the presence of the nanoparticles (in-situ synthesis). In this case, we obtained one catalyst which performed as well as the Lindlar catalyst although the metal content was slightly lower and our catalyst contained no Pb. Another catalyst of the same series, prepared in the presence of another stabilizer, performed as well as the NanoSelect™ catalyst but at a 7 times higher metal content. For the sake of comparison we also impregnated FDU-12 via classical incipient wetness impregnation and again obtained a completely nonselective catalyst. Our results demonstrate that the in-situ synthesis has great potential as regards the development of novel catalysts.

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