Diamine functionalized gel-type resin as a support for palladium catalysts: Preparation, characterization and catalytic properties in hydrogenation of alkynes

Abstract

Gel-type resin (FCN) obtained as a result of copolymerization of glycidyl methacrylate (20 mol%), styrene (77 mol%) and ethylene glycol dimethacrylate (3 mol%) and functionalized by amine groups is studied as the support for Pd-catalysts (0.5–2 wt% Pd). Pd/FCN catalysts are characterized by number of techniques (FTIR, UV–Vis, XPS, SEM and HRTEM) and tested in the hydrogenation of alkynes, 2-butyne-1,4-diol (B3-D) and phenylacetylene (Phc). Catalysts are prepared by incorporation of palladium to the swollen particles of FCN resin using THF solution of Pd(OAc) 2. In these conditions N and carbonyl groups of FCN polymer are involved in the bonding of Pd 2+ ions. This leads to decrease in swelling ability of polymer mass due to “crosslinking” of the polymer via Pd 2+ ions. Since the polymer-bound Pd species are only partially reduced under hydrazine treatment the reduced Pd/FCN samples swell less than pure FCN. In the reduced Pd/FCN samples, only at the lowest Pd-loading amounted to 0.5 wt% Pd, very well dispersed Pd-nanoclusters appear. At higher Pd content within the range 1–4 wt% Pd, the particles of Pd of size within the range 4–28 nm are formed and in all the samples the particles 8–16 nm in size predominate. In these catalysts, partial aggregation of Pd-nanoparticles proceeds, especially when the loading of Pd is higher than 1 wt%. The activity/selectivity behaviour of Pd/FCN catalysts is determined by the size of Pd-particles and swelling ability of polymer matrix under the catalytic run. In the presence of highly expanded catalysts with low Pd content, 0.5–1 wt% Pd, the alkynes substrates, B3-D or Phc are hydrogenated to alkene with selectivity 91–92% up to high alkynes conversion (90%). The suppression of alkene to alkane hydrogenation in the stage of alkynes is ascribed to high ability of Pd-centers to strong adsorption of alkyne substrate. It may also be related to steric hindrances of polymer in the vicinity of active Pd-centers caused by the swollen polymer network.