Abstract

The selective hydrogenation of 1,3-butadiene to 1-butene represents a pivotal process in the purification of industrial olefin streams, yet its performance is often hindered by undesired 1-butene isomerization to 2-butene. Herein, we employ parahydrogen-induced polarization (PHIP) nuclear magnetic resonance (NMR) spectroscopy as a pathway-sensitive probe to unravel the mechanistic origin of this isomerization. Pd−Au alloy nanoparticles supported on TiO2 with systematically tuned Pd/Au mass fractions reveal a distinct mechanistic transition governing 1-butene reactivity. Combined PHIP NMR, CO diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS), and quasi-in situ X-ray photoelectron spectroscopy (XPS) analyses demonstrate that on contiguous Pd ensembles, 1-butene isomerization is primarily driven by hydrogen surface coverage. Progressive incorporation of Au into the alloy disrupts these Pd ensembles, generating isolated Pd sites that shift the reaction control toward a competitive adsorption regime, wherein preferential 1,3-butadiene adsorption effectively suppresses 1-butene isomerization. Under reaction conditions, carbonaceous restructuring further stabilizes the single-atom Pd species, reinforcing the inhibition of isomerization.

文章链接：https://pubs.acs.org/doi/10.1021/acscatal.6c02116