Hydrogen peroxide (H2O2) is an important disinfectant and bleach and is currently manufactured from an indirect process involving sequential hydrogenation/oxidation of anthaquinones. However, a direct process in which H2 and O2 are reacted would be preferable. Unfortunately, catalysts for the direct synthesis of H2O2 are also effective for its subsequent decomposition, and this has limited their development. We show that acid pretreatment of a carbon support for gold-palladium alloy catalysts switches off the decomposition of H2O2. This treatment decreases the size of the alloy nanoparticles, and these smaller nanoparticles presumably decorate and inhibit the sites for the decomposition reaction. Hence, when used in the direct synthesis of H2O2, the acid-pretreated catalysts give high yields of H2O2 with hydrogen selectivities greater than 95%.

Hydrogen peroxide is a major commodity chemical produced currently by using an indirect process. A direct process (Scheme 1, path a) would be preferred and palladium catalysts [2][3][4][5] have demonstrated catalytic activity for such a process; recently we have shown that the addition of gold to palladium improves the catalyst performance. [6][7][8] The major problem associated with the direct synthesis of H 2 O 2 is the decomposition (Scheme 1, path d) or hydrogenation (Scheme 1, path c) of H 2 O 2 by the catalysts used for its formation.To overcome the problem of these sequential reactions with palladium catalysts stabilizers are required; [3,5] these are typically mineral acids and halides. However, the presence of stabilizers in the reaction medium pose serious problems since they have to be removed from the product after the reaction, especially when the effluent H 2 O 2 is to be used without refinement (e.g., epoxidation of propylene). We have found that for Au-Pd catalysts the addition of a halide and acid promoters is not required.[9] However, H 2 selectivities for these catalysts are at best 80 % under typical reaction conditions, which involve reactions at sub-ambient temperatures (ca. 2 8C).[7] Improvements in selectivity are now required so that the catalysts can be used at higher temperatures without loss of performance.Herein we show that the pretreatment of a TiO 2 support with acid prior to the addition of the metals leads to a catalyst which gives improved selectivity and activity. We have previously shown that for a carbon-supported Au-Pd catalyst, the acidic pretreatment [8] results in an increase in the activity for the direct synthesis of hydrogen peroxide. Most importantly, we show herein for the first time that the methodology is not only applicable to metal-oxide-supported catalysts, but can be used at ambient temperature with enhanced catalyst performance; the untreated catalysts cannot be used at these temperatures.Gold, palladium, and gold-palladium catalysts supported on TiO 2 were prepared by using wet impregnation. We also investigated the effect of acidic pretreatment of the TiO 2 prior to the impregnation of the metals onto the support (see the Supporting Information). This pretreatment step consists of suspending TiO 2 in a 2 wt % aqueous HNO 3 solution for three hours and subsequent washing (thoroughly with approximately 1 L H 2 O) and then drying (120 8C).

Hydrogen peroxide is a major commodity chemical produced currently by using an indirect process. A direct process (Scheme 1, path a) would be preferred and palladium catalysts [2][3][4][5] have demonstrated catalytic activity for such a process; recently we have shown that the addition of gold to palladium improves the catalyst performance. [6][7][8] The major problem associated with the direct synthesis of H 2 O 2 is the decomposition (Scheme 1, path d) or hydrogenation (Scheme 1, path c) of H 2 O 2 by the catalysts used for its formation.To overcome the problem of these sequential reactions with palladium catalysts stabilizers are required; [3,5] these are typically mineral acids and halides. However, the presence of stabilizers in the reaction medium pose serious problems since they have to be removed from the product after the reaction, especially when the effluent H 2 O 2 is to be used without refinement (e.g., epoxidation of propylene). We have found that for Au-Pd catalysts the addition of a halide and acid promoters is not required. [9] However, H 2 selectivities for these catalysts are at best 80 % under typical reaction conditions, which involve reactions at sub-ambient temperatures (ca. 2 8C). [7] Improvements in selectivity are now required so that the catalysts can be used at higher temperatures without loss of performance.Herein we show that the pretreatment of a TiO 2 support with acid prior to the addition of the metals leads to a catalyst which gives improved selectivity and activity. We have previously shown that for a carbon-supported Au-Pd catalyst, the acidic pretreatment [8] results in an increase in the activity for the direct synthesis of hydrogen peroxide. Most importantly, we show herein for the first time that the methodology is not only applicable to metal-oxide-supported catalysts, but can be used at ambient temperature with enhanced catalyst performance; the untreated catalysts cannot be used at these temperatures.Gold, palladium, and gold-palladium catalysts supported on TiO 2 were prepared by using wet impregnation. We also investigated the effect of acidic pretreatment of the TiO 2 prior to the impregnation of the metals onto the support (see the Supporting Information). This pretreatment step consists of suspending TiO 2 in a 2 wt % aqueous HNO 3 solution for three hours and subsequent washing (thoroughly with approximately 1 L H 2 O) and then drying (120 8C).

catalysts for direct synthesis of H2O2 from H2 and O2 are prepared by incipient wetness impregnation of TiO2 with aqueous solutions of PdCl2 and/or HAuCl4 (drying at 110°C, 16 h; calcination at 400°C, 3 h). Supports are pre-treated either with water or dilute aqueous HNO 3 for 3 h at ambient temperature. For the acid-pretreated Au-Pd/TiO2 catalyst, the H2 selectivity increases to approximately 95%, which represents a significant improvement over the H2 selectivity of about 70% for the untreated catalyst. Furthermore the calcined acid-pretreated catalysts can be reused several times without any loss of performance. -(EDWARDS, J. K.; NTAINJUA N, E.; CARLEY, A. F.; HERZING, A. A.; KIELY, C.

Catalysts H 2000Switching Off Hydrogen Peroxide Hydrogenation in the Direct Synthesis Process.-Whereas all catalysts so far identified for direct H 2 O 2 synthesis are equally effective for its sequential hydrogenation or decomposition to water, acid-pretreated Au-Pd/C catalysts give high yields of H2O2 with hydrogen selectivities greater than 95%. The acid treatment decreases the size of the alloy nanoparticles, and these smaller nanoparticles presumably decorate and inhibit the sites for the decomposition reaction. It is expected that the process using powdered catalysts in a small-scale batch autoclave reactor can be scaled up using continuous flow reactors to produce H2O2 at the 3 to 8% concentration levels required in most chemical and medical applications. In particular, the process lends itself to small-scale generation of H2O2, which could be of great value for the production of medical antiseptics. -(EDWARDS, J. K.; SOLSONA, B.; NTAINJUA N, E.; CARLEY, A. F.; HERZING, A. A.; KIELY, C. J.; HUTCHINGS*, G.

Polycyclic Aromatic Hydrocarbons (PAHs) are a group of Volatile Organic Compounds (VOCs), which have serious health problems associated with their emission into the atmosphere. Catalytic oxidation is an effective abatement process to control PAH emissions, and the types of catalysts investigated have been reviewed. The majority of studies have used naphthalene as a model PAH, and in particular, catalysts containing palladium and platinum have demonstrated high activity for total oxidation. Catalysts based on the precious metals include those supported on high surface area supports, which have also been modified by adding further components, and metal exchanged zeolites. Metal oxide catalysts have also been employed and the most active for total oxidation are ceriabased. Studies of PAH total oxidation have largely been reported only in the last 10 years, and there still remains wide scope to develop improved catalysts and understand their catalytic mechanisms.