Structure sensitivity of selective acetylene hydrogenation over the catalysts with shape-controlled palladium nanoparticles

Abstract

The structure sensitivity of acetylene hydrogenation on catalysts with controlled shape of palla dium nanoparticles was studied. Palladium particles of cubic (Pd cub ), cuboctahedral (Pd co ) and octahedral (Pd oct ) shapes were obtained by a colloidal method. Poly(N vinyl)pyrrolidone (PVP) was used as the stabi lizer of colloidal solutions. In order to eliminate the effect of the polymer on the properties of the catalyst, PVP was removed from the surface of the particles after their transfer to the support by simultaneous treat ment with ozone and UV radiation. This allowed complete cleaning of the catalyst surface from the organic stabilizer without any change in the morphology of particles. The effectiveness of this treatment method was confirmed by X ray photoelectron spectroscopy and scanning electron microscopy. It was found experimen tally that the shape of nanoparticles does not influence the catalyst selectivity, but the activity decreases in the order Pd oct > Pd co > Pd cub . Since octahedrons consist of (111) faces, the cubes contain only (100) faces, and the cuboctahedrons are composed of faces of both types, Pd 111 is more active than Pd 100 . Calculations with the use of a statistical method showed that the ~3 nm Pd octahedrons are nanoparticles with optimum shape and size, giving maximum catalyst activity.

Recent advances in selective acetylene hydrogenation using palladium containing catalysts

“…Catalyst testing under non-competitive conditions indicated that particle shape had no impact on selectivity ( Fig. 2) at an equivalent degree of conversion [29]. However, results indicated that turnover frequency (TOF) increased in the order cubes < cuboctahedra < octahedra implying that (111) faces are more active than (100) faces (note: different particle size).…”

“…Similarly, it is important to acknowledge that activity may vary with particle size therefore comparing activity of different particle shapes and sizes may, on occasion, lead to misleading results. Yarulin et al [29] systematically studied the influence of Pd particle shape on acetylene hydrogenation by preparing well defined Pd cubes [(100) faces], cuboctahedra [(100) and (111) faces] and octahedra [(111) faces]. The different morphologies were cleaned using UV light/ozone which has been shown to be an effective way to remove surface residues without altering particle shape [30] -therefore eliminating one potential source of influence from the study.…”

“…Conditions: 13% conversion and 393 K. 'Pd cub ' denotes cubic shape, 'Pd co ' denotes cuboctahrdal shape and 'Pd oct ' denotes octahedral shape. Reproduced from reference [29] with kind permission from Springer Science and Business Media Kim et al [31] also studied the effect of particle morphology starting with Pd nanocubes which could be converted into mainly spherical particles [mixture of (100) and (111) faces] by heating to 463 K. Catalyst testing revealed that the TOF for the cubes was higher than the spherical particles, contrary with the earlier report [29]. In this case, it was reported that over-hydrogenation was less significant over the cubes compared with spheres.…”

Size and Shape‐controlled Pd Nanocrystals on ZnO and SiO2: When the Nature of the Support Determines the Active Phase

“…5 The effects of shape, however, have been far less addressed. Although there are several theoretical studies of acetylene hydrogenation on single planes,4, 6 there are only a handful of experimental results dealing with real catalysts, where the TOF was found to depend on the crystallographic plane exposed, showing activities Pd(1 1 1)>Pd(1 0 0),5c or correlating the catalytic response to the number of crystal boundaries present in a Pd nanowire 7…”

The influence of alumina phases on the performance of the Pd–Ag/Al2O3 catalyst in tail-end selective hydrogenation of acetylene

“…The nature of alumina phases have been very poorly understood in catalysis because of their lower crystallinity [7]. Catalytic performance of alumina supports depends upon the alumina structure, and its active site interactions may be considered in terms of adsorption strength, particle charging and sizes, formation of multi-functional active sites, changes in particle morphology, and dispersion of active sites [2,[8][9][10].…”