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

Do not forget the classical catalyst poisons: The case of biomass to glycols via catalytic hydrogenolysis

“…Although it was not an initial objective of this study, we also estimated the maximum S coverage of Raney to get an idea of the mode of deactivation, see Section 1.7 in Appendix S1. The limit of ~2700 mmol S per kg Raney Ni is much higher than the onset for deactivation seen between 67 and 200 mmol S per kg Raney Ni and the cut‐off in activity at ~400 mmol S per kg Raney Ni seen in the study by Philippov et al ., 29 who studied the transfer hydrogenation of camphor using 2‐propanol at 82°C. This advocates that the Raney Ni surface is composed of ‘active sites’ over which the hydrogenation reactions occur.…”

Cellulosic Glycols: Identification and Prevention of Catalyst Deactivation

“…Although it was not an initial objective of this study, we also estimated the maximum S-coverage of Raney to get an idea of the mode of deactivation, see Appendix C.1.7. The limit of ∼2700 mmol S per kg Raney nickel is much higher than the onset for deactivation seen between 67 and 200 mmol S per kg Raney nickel and cut off in activity at ∼400 mmol S per kg Raney nickel seen in the study by Philippov et al [118] , who studied the transfer hydrogenation of camphor by 2-propanol at 82 • C. This advocates that the Raney nickel surface is composed of "active sites" over which the hydrogenation reactions occur. However, our experimental design is not optimal for this research objective as hydrogenation reactions compete with irreversible thermal side reactions.…”

“…The onset for a drop in yield might therefore occur before complete deactivation of the Raney nickel catalyst. C.2 Comparison with study by Philippov et al [118] Philippov et al [118] studied the transfer hydrogenation of camphor using 2propanol over Raney nickel at 82 • C and thereby investigated the impact of catalyst poisons in particular S-containing components. They ran a series of experiment in which the thiophenol loading was varied, with increase in thiophenol load and thus S to Ni ratio a decrease in camphor conversion was observed, see Figure C.8.…”

“…There is a particular sharp drop in the camphor conversion from 12 to 0 wt.% from 320 to 420 mmol S per kg of Ni, indicating that the catalyst is completely deactivated when this S to Ni ratio is exceeded. [118] . Reaction conditions: transfer hydrogenation using 2-propanol at 82 • C.…”

“…Figure C.8: Camphor conversion as function of thiophenol present in the reactionmixture expressed as sulphur / metal catalyst ratio in the study by Philippov et al[118] . Reaction conditions: transfer hydrogenation using 2-propanol at 82 • C.…”