Gas-Phase Catalytic Hydrogenation/Isomerization in the Transformation of 3-Butyn-2-ol over Pd-Ni/Al2O3

The continuous gas-phase (P = 1 atm; T = 373 K) hydrogenation of 3- butyn-2-ol has been investigated over Pd/Al2O3 and Ni/Al2O3 prepared by incipient wetness impregnation and Pd-Ni/Al2O3 (Pd/Ni mol ratio = 1:1) synthesized by co- impregnation. A physical mixture (Pd/Al2O3 + Ni/Al2O3; Pd/Ni = 1:1) is also considered for comparison purposes. H2 temperature-programmed reduction (TPR) results are consistent with a lower temperature requirement for the reduction of palladium and nickel in the bimetallic catalyst relative to the monometallic counterparts. The Pd/Al2O3 catalyst exhibits a narrow metal particle size distribution (mean = 20 nm) while Ni/Al2O3 and Pd-Ni/Al2O3 bore larger particles (mean = 28 +/- 2 nm). TEM-EDX, XRD, and XPS measurements are consistent with a palladium surface-enriched Pd-Ni bimetallic phase. Ni/Al2O3 promoted exclusive -C C- group hydrogenation to generate 3-buten-2-ol (partial reduction) and 2-butanol (complete reduction). Pd/Al2O3 exhibited a greater H-2 uptake and delivered a higher 3-butyn-2-ol transformation rate, yielding 3-buten-2-ol, 2-butanol, and 2-butanone through hydrogenation and double bond migration. An equivalent H-2 uptake, rate, and product distribution were delivered by Pd/Al2O3 and the Pd/Al2O3 + Ni/Al2O3 system, where the catalytic response was controlled by the palladium component. In contrast, we recorded a higher hydrogen chemisorption on Pd-Ni/Al2O3 (vs Pd/Al2O3) and catalytic activity with an enhanced selectivity to 3-buten-2-ol (up to 95%). We linked the distinct response over Pd-Ni/Al2O3 to the formation of bimetallic Pd-Ni as proven by TPR, XRD, TEM-EDX, and XPS analyses. A parallel/stepwise kinetic model has been used to quantify the catalytic hydrogenation response.

Automated summary

The study investigated the continuous gas-phase hydrogenation of 3-butyn-2-ol over different catalysts, with Pd-Ni/Al2O3 demonstrating higher catalytic activity and selectivity, enriched with a palladium surface in the bimetallic Pd-Ni formation. The catalytic response of Pd/Al2O3 and Pd/Al2O3 + Ni/Al2O3 is controlled by the palladium component, while Ni/Al2O3 promotes the hydrogenation of the -C C- group.