(682c) Single Ni2+ Active Sites Isolated on Polyoxometalates for Light Olefin Oligomerization

Oligomerization of light alkenes to liquid fuels and value-added products is an important reaction to upgrade domestic shale gas and biomass-based feedstocks. To overcome the inherent limitations of homogeneous catalysts based on nickel complexes, numerous efforts have been reported to tailor Ni(II)-based solid catalysts for this reaction, particularly with MOFs and zeolites. Nevertheless, MOFs suffer from lower thermal resistance and often require the use of toxic co-catalysts. Alternatively, zeolites deactivate rapidly and residual Brønsted acidity promotes cracking and skeletal isomerization, leading to unselective product mixtures.

To overcome these challenges, we previously reported the use of lacunary Wells-Dawson polyoxometalates as platforms to isolate single Ni²⁺ sites, which were supported on Brønsted-acid-free mesoporous SBA-15. This material was demonstrated to be versatile, regenerable, and unaffected by the presence of feed contaminants, showing high selectivity towards linear products both with ethylene and propylene feeds. Although the oligomerization of ethylene and propylene require different operating conditions, we have investigated the effect of co-feeding the two reactants together. Furthermore, we explored the influence of several structural and chemical modifications of the polyoxometalates on the nickel active sites, providing insights in the design of polyoxometalates-based catalysts with tailored properties. Various strategies to increase the site density have also been explored, in order to overcome the limitations of dispersing the bulky structure of polyoxometalates on the supports. Lastly, we discuss our efforts incorporating Ni active sites in Anderson-Evans polyoxometalates through a one-pot synthesis, that significantly simplifies the production of the catalyst. Further, the smaller dimensions of this structure allows better catalyst dispersions and potentially higher loadings. Overall, this work highlights the synthetic versatility of POMs for light olefin oligomerization and points to new opportunities for catalyst discovery.