Evolution of palladium sulfide phases during thermal treatments and consequences for acetylene hydrogenation

Abstract

Unsupported, bulk phase palladium sulfide has been studied for the selective hydrogenation of acetylene. The sample underwent significant change during thermal pretreatments, the extent of which depends on temperature. Exposure to hydrogen at temperatures of 150°C or above results in the loss of sulfur from the sample, primarily as hydrogen sulfide. As sulfur is lost, the sample is progressively transformed from a sulfur rich phase (PdS) to a sulfur lean phase (Pd4S) via an intermediate phase (Pd16S7). Reduction at 250°C produces a material, which contains simultaneously these three phases mentioned above with some Pd4S phase is located at the surface, whereas reduction at 350°C results in a largely pure Pd4S phase. Thermal treatments which produce a Pd4S surface display excellent catalytic properties. At complete acetylene conversion at 250°C, ethylene selectivites of 82.8% and 90.0% were obtained under non-competitive and competitive conditions, respectively. Beneficial catalytic properties arise from the uniformity of Pd sites due to the crystal structure of Pd4S along with electronic influences on the adsorption/desorption processes arising from sulfur neighbours. No indications of deactivation or obvious deposition of carbon were observed over Pd4S sample after 50 h on stream.

Comparison of Pd and Pd4S based catalysts for partial hydrogenation of external and internal butynes

“…The loss of sulfur has been verified by TPR-MS studies whereas the formation of Pd4S was followed by in-situ HEXRD [34]. An equivalent transformation has also been observed for an unsupported bulk phase palladium sulfide sample [40]. Typical TEM images of Pd4S/CNF sample are shown in Figure 1D-F along with a narrower particle size distribution (Figure 1D -inset).…”

Activation and Spillover of Hydrogen on Sub‐1 nm Palladium Nanoclusters Confined within Sodalite Zeolite for the Semi‐Hydrogenation of Alkynes

“…This process can be suppressed by alloying Pd with other metals such as Ag, Cu, or Au . Controlling the morphologies and modifications with ligands have also been used to enhance the performance of Pd‐based catalysts. This phenomenon is often explained in terms of reducing the adsorption energy of ethylene by electronic and/or geometric effects .…”

Activation and Spillover of Hydrogen on Sub‐1 nm Palladium Nanoclusters Confined within Sodalite Zeolite for the Semi‐Hydrogenation of Alkynes

“…[3][4][5] This process can be suppressed by alloying Pd with other metals such as Ag, Cu, or Au. [6][7][8] Controlling the morphologies [5] and modifications with ligands [9][10][11] have also been used to enhance the performance of Pd-based catalysts.T his phenomenon is often explained in terms of reducing the adsorption energy of ethylene by electronic and/or geometric effects. [12,13] In addition, carbon monoxide has been used as am odifier to compete with ethylene for adsorption sites, which can improve the ethylene selectivity of supported Pd catalysts.…”