Ligand-stabilized Pt nanoparticles (NPs) as novel materials for catalytic gas sensing: influence of the ligand on important catalytic properties

Abstract

Different mono- and bifunctional amine ligands have been used to stabilize Pt NPs for catalytic H2 gas sensing. Depending on the chemical structure and properties of the ligand, the catalysts show different overall sensor performances, activation periods, and long-term stabilities. These sensor characteristics are put into relation with chemical processes like cleaning of the surface, degradation processes of the ligands and nanoparticle (NP) sintering. It has been found that during activation free adsorption sites are formed primarily due to desorption of synthetic residues. Furthermore, partial desorption of the ligands followed by their degradation may occur. For monoamines the latter process results in destabilization of the NPs followed by catalyst deactivation through particle sintering. The use of bifunctional ligands that link individual NPs shows significantly enhanced stabilities which can be related to the reduction of the ligand desorption rates and degradation. Besides the functionality of the ligands it was observed that the chemical nature of their hydrocarbon skeleton affects the catalyst stability: aromatic substructures remain intact upon H2 oxidation, while alkyl fragments undergo oxidation and decomposition. The advantages of bifunctionality and an aromatic hydrocarbon skeleton can be combined by the use of para-phenylenediamine (PDA) as a linking ligand. Networks formed by this ligand were indeed found to be stable under the applied catalytic conditions for more than 24 h.

Beyond Active Site Design: A Surfactant‐Free Toolbox Approach for Optimized Supported Nanoparticle Catalysts

“…In their seminal work published in 2000, [14] Wang and co‐workers showed that precious metal nanoparticles could easily be obtained without surfactant in alkaline ethylene glycol by reduction of H 2 PtCl 6 upon heat treatment and early on it was suggested and shown that such surfactant‐free synthesis is ideal to develop readily active catalysts [15,16,26] . Surfactant‐free metal NPs like Pt, [14] Ru, [14] Rh, [14] Co, [27] Os, [15] and alloys like PtRu, [4] PtFe, [28] PtSn, [29] PtRh [15] were obtained and demonstrated in applications ranging from chemical synthesis, [15,27,30,31] to electrochemical reactions like the oxygen reduction reaction [13] or electro‐oxidation of methanol [4,28] and ethanol [29] . One of the major advantages of surfactant‐free NP is that there is no need to activate them before catalysis and the synthesis is performed are relatedly low temperature, typically 150–160 °C for a thermally induced synthesis.…”

“…The polyol synthesis is therefore a suitable approach for the toolbox, in particular due to its compatibility for electrochemical applications where free surfaces (further detailed in the Characterization section) are essential to allow an optimized electron transfer to/from the catalysts from/to the reactants. Furthermore, if the effect of surfactants or ligands should be studied, the NPs prepared by the surfactant‐free approach can thereafter be functionalized with different ligands [31,32] . This is simply achieved by performing phase transfer experiments.…”

Controlled Synthesis of Surfactant‐Free Water‐Dispersible Colloidal Platinum Nanoparticles by the Co4Cat Process

“…Unprotected NPsa re stabilized by CO and OH À groups,w hich do not requireh arsh treatments for removal. [31] The thus-obtained NPs are ac onvenient building block to investigatea nd optimize NPs such as Pt for electrocatalysis, [32] sensing, [33] or chemical transformations. [34] Alkalinee thylene glycol (EG) has long been considered the most suitable solvent for the widelyu sed polyol process.…”

Pt and Pd Nanoparticles Immobilized on Amine-Functionalized Hypercrosslinked Porous Polymer Nanotubes as Selective Hydrogenation Catalyst for α,β-Unsaturated Aldehydes

“…Furthermore, well dispersion of metal NPs were shown from elemental mapping images, as given in Figure . Unlike uncapped NPs on unfunctionalized supports, we believe that Pd/Pt NPs@PP‐3 might be stable and useful on account of the stabilization imparted by amine / alkoxy functionality of hypercrosslinked PP‐3 …”

“…Unlike uncapped NPs on unfunctionalized supports, we believe that Pd/Pt NPs@PP-3 might be stable and useful on account of the stabilization imparted by amine / alkoxy functionality of hypercrosslinked PP-3. [21] Powder X-ray diffraction (PXRD) of Pd@PP-3 and Pt@PP-3 shows the presence of broad peak at~2q = 208, corresponds to amorphous carbon peak ( Figure 3a). In addition, the presence of metal nanoparticles were confirmed from the appearance of several broad and weak intensity peaks.…”