The Direct Synthesis of Hydrogen Peroxide Over Supported Pd-Based Catalysts: An Investigation into the Role of the Support and Secondary Metal Modifiers

Abstract

The direct synthesis of H2O2 from molecular H2 and O2 over Pd-based catalysts, prepared via an industrially relevant, excess chloride co-impregnation procedure is investigated. Initial studies into the well-established PdAu system demonstrated the key role of Pd: Au ratio on catalytic activity, under conditions that have previously been found to be optimal for H2O2 formation. Further investigations using the optimal Pd: Au ratio identified the role of the catalyst support in controlling particle size and Pd oxidation state and thus catalytic performance. Subsequently, with an aim to replace Au with cheaper alternatives, the alloying of Pd with more abundant secondary metals is explored. Graphical Abstract

Enhancing the Chemo-Enzymatic One-Pot Oxidation of Cyclohexane via In Situ H2O2 Production over Supported Pd-Based Catalysts

“…However, this improvement in catalyst selectivity did not result in a concurrent increase in H 2 O 2 synthesis rates, with the 0.5%Pd–0.5%Au/TiO 2 (85 mol H 2 O 2 kg cat –1 h –1 ) and 1%Pd/TiO 2 (88 mol H 2 O 2 kg cat –1 h –1 ) catalysts offering comparable activities. While this may not have been expected given the large number of studies into PdAu systems, which have typically reported a significant improvement in H 2 O 2 synthesis upon formation of the alloy, this observation aligns well with our previous studies into identically prepared catalysts and is attributed to the application of a reductive heat treatment during catalyst preparation, and the resulting formation of nanoparticles consisting of a random alloy composition . Indeed, in many earlier studies, the use of an oxidative heat treatment, and the resulting formation of Au-core, Pd­(oxide)-shell nanoparticle morphologies has been shown to be key in achieving enhanced selectivity toward H 2 O 2 . , It is noteworthy that while the activity of the 0.5%Pd–0.5%Au/TiO 2 catalyst toward H 2 O 2 synthesis did not exceed that of the 1%Pd/TiO 2 catalyst, there was a considerable improvement compared to the 0.5%Pd/TiO 2 analogue (68 mol H 2 O 2 kg cat –1 h –1 ), which consists of an identical Pd loading.…”

“…In keeping with previous reports, 29−31 32 this observation aligns well with our previous studies into identically prepared catalysts and is attributed to the application of a reductive heat treatment during catalyst preparation, and the resulting formation of nanoparticles consisting of a random alloy composition. 33 Indeed, in many earlier studies, the use of an oxidative heat treatment, and the resulting formation of Au-core, Pd(oxide)-shell nanoparticle morphologies has been shown to be key in achieving enhanced selectivity toward H 2 O 2 . 34,35 It is noteworthy that while the activity of the 0.5%Pd−0.5%Au/TiO 2 catalyst toward H 2 O 2 synthesis did not exceed that of the 1%Pd/TiO 2 catalyst, there was a considerable improvement compared to the 0.5%Pd/ TiO 2 analogue (68 mol Hd 2 Od 2 kg cat −1 h −1 ), which consists of an identical Pd loading.…”

Surfactant- and Ligand-Free Synthesis of Platinum Nanoparticles in Aqueous Solution for Catalytic Applications

“…H2O2 decomposition is catalyzed at two different pH values, 7 and 10, by our borohydride-stabilized Pt nanoparticles at 25°C. The rate of reaction is determined by acidified Ce(SO4)2 titrations, as has been utilized previously in the literature to measure H2O2 synthesis and decomposition rates [27,[45][46][47]. Further details of the titrations are included in Section 3.5.…”

Chemo‐Enzymatic One‐Pot Oxidation of Cyclohexane via in‐situ H2O2 Production over Supported AuPdPt Catalysts

“…The alloying of Pd with a range of secondary metals, [15][16][17][18] particularly Au, [19][20][21][22] has been extensively studied and demonstrated to improve catalytic reactivity and selectivity towards H 2 O 2 synthesis when studied under optimised reaction conditions. These enhancements are often attributed to the modification of Pd oxidation states and the disruption of contiguous Pd domains.…”