Sulfur adsorption and release properties of bimetallic Pd–Ni supported catalysts

• Stabilization of Ni on catalyst surface by formation of spinel structure.
• Solvent concentration affects the ratio between NiO and NiAl2O4 in Pd–Ni catalyst.
• Co-impregnated Pd–Ni catalysts produce less H2S than mixture of NiO with Pd/Al2O3.
• Addition of La to catalysts increases amount of H2S released.
• Pd–Ni catalysts prepared from diluted solvent produce less H2S.

The formation of hydrogen sulfide in car exhaust is undesirable due to unpleasant odor and toxicity of H2S gas. H2S release can be suppressed by the addition of a NiO scavenger to a three-way catalyst (TWC). In this work, Pd–Ni bimetallic catalysts were prepared by the co-addition of Pd and Ni to γ-Al2O3 or Al2O3-La2O3 support, by the impregnation method. Different concentrations of a propionic acid aqueous solution were used as the impregnation solvent. The structure of prepared catalysts was characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), and temperature-programmed reduction (TPR) techniques. Catalyst poisoning by SO2 was simulated under lean conditions and H2S release under rich conditions. XRD and TPR measurements revealed the effect of the impregnation solvent concentration on the ratio between NiO and NiAl2O4 spinel species and the reducibility of Ni species. Co-addition of Pd with Ni was proven to be beneficial for H2S suppression. Prepared bimetallic catalysts released considerably less H2S compared to physical mixtures of Pd/Al2O3 with NiO. The presence of bulk and well dispersed NiO on Pd–Ni catalysts assisted in sulfur release in the form of sulfur oxides rather than H2S. Bimetallic catalysts supported on Al2O3-La2O3 were found to release more H2S compared to catalysts on γ-Al2O3. The use of diluted solvent in bimetallic catalysts preparation decreased H2S release from Pd–Ni catalysts.

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