Palladium-platinum powder catalysts manufactured by colloid synthesis

Abstract

Unsupported Pd, Pt and PdPt bimetallic catalysts were prepared in different atomic ratios using methods of colloid chemistry. They were characterized by XPS, UPS and TEM. Four subsequent treatments with O 2 and H 2 up to T = 603 K were applied in the preparation chamber of the electron spectrometer and before the catalytic runs. Platinum strongly hindered the oxidation of palladium in the bimetallic samples indicating an alloying of the two components. The H 2 treatment after O 2 led to rather clean metals. These treatments up to 603 K decreased the Pt enrichment near to the surface found by XPS, destroying presumably the Pt islands on the surface of a Pd-rich matrix. The particle composition approached thus a homogeneous metal mixture. The catalytic behavior was tested in the hydrogenative ring opening reaction of cisand trans-methyl-ethylcyclopropane (MECP) at 373 K. The product ratios 2-methylpentane/3-methylpentane (2MP/3MP) and 2-methylpentane/n-hexane (2MP/nH) were used to characterize the ring-opening pattern of the samples. The bimetallic catalysts revealed higher activity and completely different selectivities than the monometallic Pt and Pd. Moreover, the 2MP/3MP ratio from trans-MECP and 2MP/nH ratio from cis-MECP increased as the surface Pt enrichment decreased. PdPt catalysts were cleaner than Pd or Pt, their activity higher and selectivity closer to random CC rupture, due, very likely, to the presence of active Pd-Pt ensembles.

Palladium-platinum powder catalysts manufactured by colloid synthesis

“…Treating the samples with H 2 at 473 K represented a customary cleaning process for Pt [34] and Pd [37], although the cleanest metals were observed after a more severe purification process (O 2 and H 2 treatment [34]). Such results will be reported in Part II [32]. Table 2 indicates that even the present treatment brought the Pd:Pt ratio closer to the nominal values.…”

“…The effect of oxidation-reduction cycles on crystallite sizes, composition as well as their catalytic behaviour in the ring opening reaction of methylethylcyclopropane is going to be reported in a subsequent paper [32].…”

Structures of small Pd–Pt bimetallic clusters by Monte Carlo simulation

“…Long-term stability tests confirmed the excellent stability and good quality of the supported Pd-Pt bimetallic catalysts [7]. Also, Pd-Pt bimetallic catalysts are widely known as excellent catalysts for the wet oxidation of the reactive dyes [8], hydrodechlorination of dichlorodifluromethane [9], hydrogenative ring opening reaction [10] and combustion of methane [11]. More importantly, Pd-Pt bimetallic clusters attract much attention to their structures on the nanometer scale, due to their well defined and controllable properties.…”

In situ investigation of Pt100−xAuxand Pt100−ySnynanoalloys

“…69 Certainly Pd-Pt surfaces have been studied using the 2MP/3MP ratio arising from conversion of cis or trans methyl-ethyl-cyclopropane (MECP) and MCP. 70,71 Of course one could also consider 2MP/hexane product ratios for MCP conversion, but to enable both reactions to be followed in the same way only 2MP/3MP ratios in the products of MCP and n-hexane conversion were considered here.…”