Selectivity patterns in heterogeneously catalyzed hydrogenation of conjugated ene-yne and diene compounds

Selectivity control in heterogeneously catalyzed hydrogenation of conjugated hydrocarbons (ene-yne and diene compounds) is a challenging task. Available studies on the topic mainly encircle 1,3-butadiene as the substrate and palladium as the catalyst, while more elaborated playground molecules and other metals remain largely unexplored. This study investigates the gas-phase hydrogenation of valylene (2-methyl-1-butene-3-yne) and isoprene (2-methyl-1,3-butadiene) over Pd, Pb-poisoned Pd, CO-modified Pd, Cu, Ni, and bimetallic CuNi catalysts. Chemoselectivity, regioselectivity, full hydrogenation, and CC bond formation/scission footprints of the catalytic systems at different inlet hydrogen-to-hydrocarbon ratios and conversion degrees have been rationalized. Complementary studies of 3-methylbutyne and 1-penten-4-yne hydrogenation were carried out in order to analyze (i) the impact of isomerization on the observed mono-olefin distribution in valylene/isoprene hydrogenation and (ii) the conjugation issue in partial ene-yne hydrogenation. Our results lead to an improved understanding of hydrogenation of polyunsaturated hydrocarbons and open doors to design more selective heterogeneous catalysts and related processes for this practically important class of reactions.

Graphical abstractSelectivity patterns in the hydrogenation of conjugated ene-yne (valylene) and diene (isoprene) compounds are determined over Pd, Cu, and Ni-based catalysts.Figure optionsDownload full-size imageDownload high-quality image (112 K)Download as PowerPoint slideHighlights► Hydrogenation of valylene, isoprene, 3-methyl-1-butyne, and 1-pentene-4-yne investigated. ► Catalysts include Pd, Pb-poisoned Pd, CO-promoted Pd, Cu, Ni, and CuNi. ► Selectivity patterns at different feed H2:hydrocarbon ratio and degree of conversion. ► Improved understanding of hydrogenation of polyunsaturated hydrocarbons.