Mechanism of carbon?nitrogen bond scission in the presence of H2S on Pt Supported catalysts

Abstract

The reactivity of a series of amines with various structures and different numbers of hydrogen atoms on the carbon atoms in the a and b position was used to evidence the C-N bond scission mechanism in the presence of H 2 S on Pt based catalysts (deposited on alumina, zirconia and silica-alumina) and compare it with the mechanism on a NiMoP on alumina sulfide catalyst. The effect of the H 2 S partial pressure was also checked. Catalytic activities (amine overall conversion, C 5 hydrocarbon formation, and amine disproportionation) deeply depend on the structure of the N-containing molecule. Tert-pentylamine is the most reactive molecule for sulfide catalysts whereas, in the case of n-pentylamine, Pt on zirconia was found to be the most efficient for C-N bond breaking. Such properties cannot be related to the acidic properties of the support but to a unique support-metal interaction, since alumina or silica-alumina supported platinum catalysts do not present this behaviour.

Hydrodeoxygenation and hydrodenitrogenation of n-hexadecanamide over Pt catalysts: effect of the support

“…99,100 The HDN of C16 amine to C16 paraffin likely occurred via a mechanism involving the dissociative adsorption of C16 amine to a hydrogen-deficient surface species on the Pt sites. 13,77,101,102 A cooperative mechanism with adsorption of C16 amine on a Lewis acid site and hydrogenolysis catalyzed by Pt, similar to the HDO of C16 alcohol, may also be possible. Brønsted acid site catalyzed Hofmann elimination of C16 amine to an olefin, followed by hydrogenation of the olefin on Pt, may have occurred in the case of Pt/30SiO 2 -70Al 2 O 3 (Fig.…”

“…This may have followed from the high concentrations of C16 nitrile and C16 amine, as Pt is highly active for the formation of secondary amines via the disproportionation of primary amines and the condensation of imines and primary amines (Scheme 1). 12,13,100,102,[105][106][107] In the case of the Ce-Zr group, C32 amine was of importance, too, but its formation through condensation of C16 alcohol and C16 amine was more favored than on the Ti-Nb group due to the significant intermediate C16 alcohol yields. 108,109 The formation of C32 amine could be catalyzed by the Pt sites, but a mechanism involving both Pt sites and Lewis acid sites of the support may also have been possible, particularly for the pathways that involved C-O bond scission (Scheme 1).…”

“…78 The HDN of C32 amine to C16 paraffin could proceed on the Pt sites, or possibly the Lewis acid and Pt sites. 13,77 The HDN of C32 amine did not seem to occur readily until the oxygen-containing intermediates had been converted, suggesting that the presence of oxygen-containing compounds inhibited the reaction (Fig. 5).…”

“…11 A high HDO activity and the ability to catalyze C-N bond hydrogenolysis make supported noble metal catalysts an alternative to transition metal sulfide catalysts for the hydrotreatment of sulfur-free feedstocks. 7,8,[12][13][14][15] In our previous study on the co-hydrotreatment of fatty acids and alkyl amines on Pt/ZrO 2 , we found that HDN was inhibited by the HDO of oxygen-containing intermediates and the formation of secondary amines and amides through condensation reactions. 16 An information gap remains for the application of noble metal catalysts in the simultaneous HDO and HDN of molecules that contain both oxygen and nitrogen and on the effect of the catalyst composition on the relative HDO and HDN activity.…”

Protein‐Rich Biomass Waste as a Resource for Future Biorefineries: State of the Art, Challenges, and Opportunities

“…The direct deamination of lysine hydrochloride with sulfided Pt/C (1 mol % Pt) in ethanol at 250 °C was even less successful, with only 15 % yield of ϵ‐caprolactam . Moreover, the reaction was performed under a reducing atmosphere containing toxic H 2 S (20 vol %) to facilitate the elimination of NH 3 , though it is known that noble metal catalysts are easily deactivated by irreversible chemisorption of reduced sulfur species . Very recently, De Vos and co‐workers developed a two‐step chemocatalytic process for the deamination of glutamic acid to dimethyl glutarate and trimethylamine .…”