Low-loading Ni/h-BN catalysts for low-temperature selective semi-hydrogenation of 1,3-butadiene to butenes: Mechanistic Insights from in situ and transient DRIFTS

Selective hydrogenation of 1,3-butadiene to butenes at low temperatures is challenged by consecutive hydrogenation of the desired products to butane. Here, a series of xNi/h-BN catalysts with Ni loadings of 0.25–1.0 wt% was prepared by impregnation to investigate loading-dependent catalytic behavior. The h-BN-supported catalyst exhibited substantially higher low-temperature conversion than its Al 2 O 3 -supported counterpart at the same nominal Ni loading. Increasing Ni loading enhanced 1,3-butadiene conversion but decreased total butene selectivity, revealing an activity–selectivity trade-off. Notably, 0.25Ni/h-BN achieved a butene yield of 60.7% with 92.2% selectivity at 70 °C, whereas 0.5Ni/h-BN delivered a comparable yield of 59.1% at 60 °C. TEM, H 2 -TPR, and XPS revealed loading-dependent changes in Ni particle size, reducibility, and surface speciation. In situ CO-DRIFTS showed less persistent CO retention over 0.25Ni/h-BN and 0.5Ni/h-BN than over the higher-loading catalysts. Transient DRIFTS further supported the adsorption and subsequent transformation of butadiene-derived unsaturated species upon H 2 introduction. Together, these results suggest that adsorbate retention and possible readsorption contribute to the stronger over-hydrogenation tendency at higher Ni loading. This work highlights the importance of balancing reactant conversion with product release in developing non-noble-metal catalysts for low-temperature selective diene hydrogenation.