Influence of the preparation conditions ofPd‐ZrO2andAuPd‐ZrO2nanoparticle–decorated functionalisedMWCNTs: Electron spectroscopy study aided with theQUASES

Abstract

The Pd, AuPd, and ZrO2nanoparticle–decorated functionalised multiwalled carbon nanotubes (f‐MWCNTs) were reported as efficient catalysts of formic acid (FA) electro‐oxidation. Different preparation conditions influence their chemical and structural properties analysed by X‐ray photoelectron spectroscopy aided with the quantitative analysis of surfaces by electron spectroscopy. Different reduction procedures such as NaBH4, a polyol microwave‐assisted method (PMWA), and a high pressure microwave reactor (HPMWR) were applied for decorating ZrO2/f‐MWCNTs with Pd and AuPd nanoparticles. The ZrO2nanoparticles are attached through oxygen groups to the surface of f‐MWCNTs. In NaBH4and HPMWR procedures, Pd nanoparticles precipitate predominantly on ZrO2of nearly nominal stoichiometry, whereas in PMWA procedure, Pd and AuPd nanoparticles precipitate predominantly on the surface of f‐MWCNTs, bridging with oxygen groups and ZrOx(x < 2) and leading to Pd‐O‐Zr phase formation. Strong reducing procedures (NaBH4and FA) led to smaller Pd nanoparticle size, Pd oxide content, and PdOxoverlayer thickness in contrary to weak reduction procedures (HPMWR and PMWA). The highest content of Pd‐O‐Zr phase appeared for Pd predominant precipitation on ZrO2nanoparticles (HPMWR) in contrary to Pd and AuPd predominant precipitation on surface of f‐MWCNTs (NaBH4 ~ FA > PMWA). Larger content of Pd‐O‐Zr phase in AuPd‐decorated ZrO2/f‐MWCNTs in contrary to Pd‐decorated sample (PMWA) could be justified by different electronic properties of nanoparticles. The FA treatment of Pd and AuPd‐ZrO2/f‐MWCNTs samples provided decreasing Pd oxide content, overlayer thickness, nanoparticle size, increasing nanoparticle surface coverage and density, amount of Pd‐O‐Zr, what results from reduction of oxygen groups bridging with Pd and ZrOxnanoparticles, also through Pd‐O‐Zr phase.