Solvent-Free Selective Hydrogenation of 2-Butyne-1,4-diol over Structured Palladium Catalyst

Hydrogenation of 2-butyne-1,4-diol catalyzed by Pd nanoparticles on activated carbon fibers (ACFs) was studied. The ACF support in the form of woven fabrics provides the basis for structured catalytic fixed beds. In the present study, this catalyst was integrated in the stirrer of an autoclave. Hydrogenations were carried out in pure, solvent-free butynediol at temps. from 352 to 392 K and hydrogen pressures of 1-2 MPa. The results were compared to those obtained for aq. solns. at different pH's and temps. of 293-333 K. High selectivities of >=98% toward 2-butene-1,4-diol at conversions of ?90% were attained in both systems. Turnover frequencies had comparable values at the same temp. The activation energy of 30 kJ/mol was detd. from initial reaction rates. Because this value is identical for the aq. soln. and the solvent-free system, mass-transfer limitations can be excluded for both systems. Concn.-time profiles were quant. predicted assuming the Langmuir-Hinshelwood kinetics with weak hydrogen adsorption. Estd. kinetic parameters allow a coherent interpretation of the exptl. observations. Catalyst reactivation and multiple reuses were demonstrated. [on SciFinder (R)]