Direct oxidation of hydrogen to hydrogen peroxide over Pd-containing fluorinated or sulfated Al2O3, ZrO2, CeO2, ThO2, Y2O3 and Ga2O3 catalysts in stirred slurry reactor at ambient conditions

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

“…As discussed previously the role of Pd oxidation state in controlling catalytic performance towards the direct synthesis of H 2 O 2 has been well studied [46,47], with the formation of domains of mixed Pd oxidation state suggested to be a key factor in achieving enhanced catalytic efficacy towards the direct synthesis of H 2 O 2 . Indeed, catalysts consisting of such domains have been reported to offer improved performance compared to those that consist predominantly of Pd 2+ or Pd 0 [39,40].…”

Looking for the “Dream Catalyst” for Hydrogen Peroxide Production from Hydrogen and Oxygen

“…Early reports by Pospelova et al in 1961 claimed that Pd 2 0 clusters were responsible for H 2 O 2 formation [18] and later other authors confirmed that Pd in a reduced state is more active and selective for H 2 O 2 formation [19]. Conversely, Choudhary and coworkers were the first to report evidence that Pd 2+ is the active center forming H 2 O 2 because it can molecularly adsorb dioxygen yielding surface peroxo species, while Pd 0 favors decomposition or over-hydrogenation of the peroxide [20]. From theoretical studies on H 2 O 2 synthesis over metallic catalysts, Sellers and co-workers [21] suggested that the formation of H 2 O 2 from H 2 /O 2 mixtures is more favorable on Au and Ag than Pt and Pd.…”

“…Among solid acid supports, regularly cited examples include acidic supports such as MoO 3 on zirconia, V 2 O 5 on zirconia, supported sulfuric acid catalysts [120,121] and fluorinated alumina [20].…”

Quantitative Insights into the Reaction Mechanism for the Direct Synthesis of H2O2over Transition Metals: Coverage-Dependent Microkinetic Modeling

“…28 Therefore, there exists a strong connection between palladium oxide and a surface with high coverage of oxygen. Complicating scientific issues is the fact that the mechanism of direct synthesis changes dynamically 18,58 with the reaction condition, resulting in significant debates on active centers among metallic Pd, 12,16,59 PdO, 60,61 and Pd/PdO mixture. 17,62−64 Especially, the ratio of H 2 /O 2 considerably changes the oxidation state of palladium further, varying the performance of catalysts, which was proposed by Kanungo et al through the in situ X-ray absorption spectroscopic investigation.…”

“…Therefore, there exists a strong connection between palladium oxide and a surface with high coverage of oxygen. Complicating scientific issues is the fact that the mechanism of direct synthesis changes dynamically , with the reaction condition, resulting in significant debates on active centers among metallic Pd, ,, PdO, , and Pd/PdO mixture. ,− Especially, the ratio of H 2 /O 2 considerably changes the oxidation state of palladium further, varying the performance of catalysts, which was proposed by Kanungo et al through the in situ X-ray absorption spectroscopic investigation . Another vital operando spectroscopy by Selinsek et al indicated that the yield of H 2 O 2 was very small in both hydrogen-lean and hydrogen-rich conditions, with the selectivity being highly dependent on the composition of the environmental atmosphere (H 2 and O 2 ) .…”