Generalized approach for the synthesis of silica supported Pd-Zn, Cu-Zn and Ni-Zn gamma brass phase nanoparticles

• Published in: Catalysis today Vol. 334; pp. 231 - 242
• Main Authors: Dasgupta, Anish, Zimmerer, Eric K., Meyer, Randall J., Rioux, Robert M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.08.2019
• Subjects: Ethylene hydrogenation; Gamma brass; Intermetallic; Ni-Zn; Pd-Zn; X-ray absorption spectroscopy; X-ray diffraction; Ethylene hydrogenation; Pd-Zn; X-ray diffraction; X-ray absorption spectroscopy; Intermetallic; Ni-Zn; Gamma brass
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2018.10.050

[Display omitted] •Pd-Zn intermetallic γ-brass phase catalysts synthesized from Pd/SiO2 catalysts.•Synthetic parameters are optimized to reduce particle size to <10 nm.•Zn inclusion negates CO binding on Pd but hydrogenation activity is retained.•Approach extended to the synthesis of Ni-Zn and Cu-Zn γ-brass nanoparticles. The existing literature suggests it is particularly difficult to access the catalytically relevant, and relatively complex, intermetallic γ-brass crystal structure through traditional nanoparticle (NP) synthesis techniques. We introduce a simple and rational approach to access this phase in M-Zn (M = Pd, Cu, Ni) systems as silica-supported single-phase nanocrystals. This hybrid approach involves the initial synthesis of supported M/SiO2 through traditional approaches (dry impregnation and strong electrostatic adsorption) followed by heating to high temperatures in the presence of a stoichiometric amount of metallic Zn in an evacuated closed system for several hours. We demonstrate the generality of this method with three different catalytically important bimetallic systems: Pd-Zn, Ni-Zn and Cu-Zn. Of these three, Pd-Zn is by the far the most popular in terms of catalytic applications and yields the smallest particle size (∼8 nm). We tested the influence of various synthesis parameters on phase purity and particle size distribution in case of the synthesized γ-brass Pd-Zn/SiO2 supported catalysts and provide general guidelines towards optimization of synthesis. Upon transformation of Pd/SiO2 to γ-brass Pd-Zn/SiO2, a precipitous drop in CO adsorption and a 25 kJ/mol increase in the ethylene hydrogenation barrier is observed, indicating the catalytic active sites are significantly modified as a result of alloying. We anticipate these catalysts may find applications in various Pd-catalyzed chemistries.