Semihydrogenation of 2-methyl-3-butyn-2-ol over PdxAg1-x/TiO2 films in microcapillary reactor: Effect of active component composition

Bimetallic catalysts based on palladium are one of the most commonly used catalysts for selective hydrogenation of triple bond. Since the Pd-Ag alloyed nanoparticles possessed low toxicity and oxidative stability, this system has been used in the selective hydrogenation of 2-methyl-3-butyn-2-ol in continuous mode. The PdxAg1-x nanoparticles (x = 0.33, 0.5, 0.63, 0.9) with controlled sizes of 4-8 nm and PdxAg1-x/TiO2 catalytic films have been prepared using polyol and sol-gel method, respectively. XRD, TEM and XPS analyses have been used to characterize the surface morphology, structure and size of active component in PdxAg1-x/TiO2. The effect of nanoparticles composition on the catalytic properties of films has been investigated in microcapillary reactor. In addition, the conditions of films pretreatment were optimized. The silver introducing leads to a decrease in the ratio of alkene to alkyne adsorption constants, a decrease in the rate constant of alkene hydrogenation to alkane, and an improvement in alkenol selectivity in all cases except for the case when Pd is a minor component (Pd/Ag = 0.5). The bimetallic catalytic films with equimolar solid solution (Pd/Ag = 1) showed the highest selectivity (98 %) relative to the monometallic Pd/TiO2 (93 %) at a deep conversion (>= 99 %). This catalyst system is also demonstrated an increase of activity during 40 h and stable activity and selectivity for the next 72 h, justifying the use of a catalytic film for the production of 2-methyl-3-buten-2-ol, which is a starting material in the manufacturing vitamins in the pharmaceutical industry.