Poisoning titration of metal nickel-based catalysts – an efficient and convenient tool to quantify active sites in transfer hydrogenation.

[Display omitted] • Poisoning titration is precise approach to quantify Raney® Ni active centers. • Effect of 15 poisons (thiols, amines, acids) on catalyst activity measured. • TOF of Raney® Ni probed by thiophenol titration was 2.4 h–1 at 82 °C. • C–S bond cleavage of thiophenol did not occur during poisoning of Raney® Ni. For the first time, the poisoning effect of 15 different chemical compounds on Raney® nickel catalyst has been comparatively studied in the transfer hydrogenation of camphor using 2-PrOH as a solvent and a hydrogen donor. It has been shown that thiophenol, HCl and H 3 PO 4 demonstrate the strongest poisoning action under the reaction conditions: no camphor conversion was observed at 5 mol.% of poison-to-nickel ratio. A strong chemical binding of thiophenol molecules to the catalyst surface without C S bond cleavage was proved by XRF, TPD methods, CHNS analysis, and FTIR spectroscopy. It was shown that the poisoning titration with thiophenol is an effective and convenient tool to calculate the number of active sites for Ni based catalysts directly, measuring catalytic activity in target chemical reaction, which was defined correspondently as 2.4 h−1 and 9.6 × 10–5 mole for Raney® nickel catalyst in the transfer hydrogenation. [ABSTRACT FROM AUTHOR]