吡啶改性Pd/SiO2催化剂用于H2和O2直接合成H2O2

引言过氧化氢(H2O2)是一种理想的绿色氧化剂,广泛应用于化学品合成、纺织、造纸、环保、食品、医药、冶金和农业等领域[1]。目前,蒽醌法[2-5]是工业上生产H2O2的主要方法。20世纪40年代,德国I.G.Farbenindustrie首先采用蒽醌法(又称Riedl-Pfleiderer法)工业化生产过氧化氢。该方法首先将2-烷基蒽醌(通常是2-乙基蒽醌)溶解于合适的有机溶剂中,溶液中的2-烷基蒽醌经催化剂催化加氢,被还原成蒽氢醌或5,6,7,8-四氢蒽氢醌,再经空气氧化得到蒽醌或四氢蒽醌和     

The Active Phase in the Direct Synthesis of H2O2 from H2 and O2 over Pd/SiO2 Catalyst in a H2SO4/Ethanol System

In an effort to determine the active state of supported palladium for the direct formation of H₂O₂ from H₂ and O₂, the catalytic behavior of Pd⁰/SiO₂, PdO/SiO₂ and partially reduced PdO/SiO₂ was determined. The results obtained in an ethanol slurry, with chloride ions and H₂SO₄ being present, showed that the PdO/SiO₂ catalyst was almost completely inactive for the formation of H₂O₂ at 10 °C. The Pd⁰/SiO₂ catalyst exhibited the highest activity for H₂O₂ formation, and the PdO/SiO₂ material, reduced under very mild conditions, exhibited an intermediate activity. The state of Pd on the three catalysts was characterized by XRD, TEM and XPS methods. Only Pd⁰ (the metal phase) and PdO were observed on Pd⁰/SiO₂ and PdO/SiO₂, respectively. As expected, with the partially reduced PdO/SiO₂ catalyst, both Pd⁰ and PdO phases were evident. The TEM results revealed that the Pd⁰ particles decorated the larger PdO particles. The results reported here support the role of metallic palladium, rather than the oxide, as the active phase for the direct formation of H₂O₂.     

Hydrogen Spillover in Ga2O3–Pd/SiO2 Catalysts for Methanol Synthesis from CO2/H2

The hydrogenation of CO₂ was investigated on Ga₂O₃-promoted Pd/SiO₂ catalyts and mechanical mixtures of Ga₂O₃/SiO₂ and Pd/SiO₂ catalysts (H₂/CO₂ = 3; P = 3.0 MPa; T = 523 K). By means of the latter it was possible to demonstrate that atomic hydrogen, H_s, can be generated by Pd⁰ far from Ga₂O₃, and move (spill-over) there to reach the other reactive species (formates) and complete the reaction cycle. The reaction results indicate that (as also evidenced by in situ FTIR) the Ga₂O₃-Pd/SiO₂ catalyst works as a true bi-functional system. The metal-promoter intimacy is not decisive in terms of the catalytic chemistry of the system, but the closeness between the Pd crystallites and the Ga₂O₃ surface patches boost the activity, owing to a minimized effort in the H_s supply to the latter.     

Pd/polyaniline(SiO2) a novel catalyst for the hydrogenation of 2-ethylanthraquinone

A novel palladium catalyst supported on silica grains coated with polyaniline (PANI) (24.4 wt% of polymer) was used for the hydrogenation of 2-ethylanthraquinone (eAQ). This 2%Pd/PANI(SiO₂) catalyst exhibited much better selectivity in the hydrogenation of eAQ to active quinones than that of 2%Pd/SiO₂ prepared by a conventional precipitation method. It is suggested that the modification of properties of Pd centres by PANI matrix, has an effect on their reactivity. The weakening of the strength of hydrogen bonding and hydrophobic character of polymer both can be considered as factors remarkably improving performance of Pd/PANI(SiO₂) catalyst.     

Mechanism of sulfur poisoning on supported noble metal catalyst — The adsorption and transformation of sulfur on palladium catalysts with different supports

A series of supported palladium catalysts (Pd/Al₂O₃, Pd/MgO and Pd/TiO₂) were prepared by the impregnating method and treated with H₂S, H₂ +O₂ or O₂, among which H₂S is used as a poison and H₂ +O₂ or O₂ are as purging atmospheres. The S^2– species in the supports was introduced by means of mechanically mixing Na₂S with the supports or catalysts. X-ray photoelectron spectroscopy (XPS) was employed to determine the changes in the chemical states of oxygen, palladium and sulfur in the catalysts before and after the treatment, while infrared (IR) spectroscopy was used to measure the SO^2– ₄ group produced in the catalysts and supports. The results show that on MgO and TiO₂ carriers whose acidities are weak, there exist two kinds of oxygen species, one is the lattice oxygen, the other one is the active species of oxygen. The latter can oxidize the S^2– into SO^2– ₄ even at room temperature in air. Because of the weak acidities and smaller specific surface area of MgO and TiO₂, the S^2– is liable to adsorb on the catalysts and to transform into SO^2– ₄. But for the case of Al₂O₃ support its acidity is rather strong, and its surface oxygen species under the experimental conditions is not so active as that in MgO and TiO₂ carries. The poison H₂S on the Al₂O₃ support only experiences a process of physical adsorption-desorption. In Pd/Al₂O₃ catalyst, the negatively charged sulfur ions are not so easily adsorbed and transformed as those in Pd/MgO and Pd/TiO₂. It is also implied that the properties of the carriers are related to the ability of self-regeneration of the corresponding catalysts. Pd/Al₂O₃ catalyst is more able to self-regenerate than Pd/MgO and Pd/TiO₂ catalyst.     

Coking and regeneration of palladium-doped H3PW12O40/SiO2 catalysts

The coking during propene oligomerisation and subsequent regeneration of both silica-supported heteropoly acid H₃PW₁₂O₄₀ (PW) and its palladium-modified form (1.6–2.5 wt% Pd) have been studied. ³¹P MAS NMR studies have revealed that the Keggin structure of the catalyst was unaffected by coke deposition in both unmodified PW/SiO₂ and Pd-modified form. As shown by ¹³C MAS NMR and TGA/TPO, the Pd modification affects the nature of the coke formed: for the standard catalyst (PW/SiO₂) both soft coke, comprising mainly high molecular weight aliphatic oligomers, and hard coke, comprising polynuclear aromatics, are formed whilst on the Pd-modified catalyst only the soft coke is observed. Coke formation causes strong deactivation of the catalyst in the oligomerisation of propene. The aerobic burning of coke on the unmodified PW/SiO₂ occurs in the temperature range of 470–520°C. Doping the catalyst with Pd significantly decreases this temperature to allow catalyst regeneration at temperatures as low as 350°C without loss of catalytic activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Size‐Dependent Catalytic Activity of Supported Palladium Nanoparticles for Aerobic Oxidation of Alcohols

Silica‐alumina (SiO₂‐Al₂O₃)‐supported palladium catalysts prepared by adsorption of the tetrachloropalladate anion (PdCl₄²⁻) followed by calcination and reduction with either hexanol or hydrogen were studied for the aerobic oxidation of alcohols. The mean size of the Pd particles over the SiO₂‐Al₂O₃ support was found to depend on the Si/Al ratio, and a decrease in the Si/Al ratio resulted in a decrease in the mean size of the Pd nanoparticles. By changing the Si/Al ratio, we obtained supported Pd nanoparticles with mean sizes ranging from 2.2 to 10 nm. The interaction between the Pd precursor and the support was proposed to play a key role in tuning the mean size of the Pd nanoparticles. The Pd/SiO₂‐Al₂O₃ catalyst with an appropriate mean size of Pd particles could catalyze the aerobic oxidation of various alcohols to the corresponding carbonyl compounds, and this catalyst was particularly efficient for the solvent‐free conversion of benzyl alcohol. The intrinsic turnover frequency per surface Pd atom depended significantly on the mean size of Pd particles and showed a maximum at a medium mean size (3.6–4.3 nm), revealing that the aerobic oxidation of benzyl alcohol catalyzed by the supported Pd nanoparticles was structure‐sensitive.     

Direct synthesis of H2O2 from H2 and O2 over Pd/H-beta catalyst in an aqueous acidic medium: Influence of halide ions present in the catalyst or reaction medium on H2O2 formation

The influence of different halide ions present in the catalyst or reaction medium on the performance of Pd/H-beta catalyst in the direct H₂O₂ synthesis in an aqueous acidic (0.03 M H₃PO₄) reaction medium at 27 °C and atmospheric pressure has been thoroughly investigated. The results showed a strong influence of both the bulk Pd oxidation state in the catalyst and the halide ions added to the reaction medium on the performance of the catalyst in the H₂ to H₂O₂ oxidation, H₂O₂ decomposition/hydrogenation reactions. The different ammonium halides impregnated reduced Pd/H-beta catalyst calcined in inert (N₂) and oxidizing (air) gaseous atmospheres also revealed that the bulk Pd oxidation state and nature of the halide ions present in the catalyst together control the overall performance of the catalyst in the H₂O₂ formation reaction. The presence of halide ions in reaction medium or in the catalyst significantly changes the selectivity for H₂O₂ formation in the direct H₂O₂ synthesis. Bromide ions are found to remarkably enhance the H₂O₂ selectivity in the direct H₂O₂ synthesis irrespective of the Pd oxidation state in the catalyst. The promoting action of Br⁻ is attributed mainly to the large decrease in the H₂O₂ decomposition and hydrogenation activities of the catalyst and also inhibition for the non-selective H₂-to-water oxidation over the catalyst.     

Role of Feed Composition on the Performances of Pd-Based Catalysts for the Direct Synthesis of H2O2

The role of feed composition, in particular the O₂ to H₂ ratio and the concentration of CO₂, has been investigated on two Pd/N-CNT and PdAu/N-CNT catalysts. There is a significant influence on the catalytic behavior, but the effect is complex, and cannot be analyzed in terms of conventional kinetic approaches, due to the presence also of a change in the catalyst characteristics as a function of time on stream (in the fresh samples). Depending on the O₂ to H₂ feed and catalyst nature, the trend of productivity and selectivity varies differently with the time on stream. A simplified kinetic model has been developed which well accounts for the observed behavior. The model is based on the concepts that (i) the selective sites are associated to small Pd terraces covered by chemisorbed O₂ with limited sites for H₂ chemisorption, and (ii) during the reaction, due to catalyst modifications, a change of available chemisorbed H₂ for unselective parallel formation of H₂O and H₂O₂ hydrogenolysis occurs. The changes during time on stream are related to (i) the removal of PVA capping agent, with an initial increase of available Pd surface area leading also to an increase of the H₂ chemisorption sites for unselective parallel conversion and consecutive H₂O₂ hydrogenolysis, and (ii) for the longer times on stream aggregation of some Pd nanoparticles leading to some decrease in the available Pd surface area. The isolation of Pd ensembles by Au (PdAu/N-CNT) influences this trend of productivity and selectivity to H₂O₂ as a function of the O₂ to H₂ ratio in the feed. The change is consistent with the model indicated above.     

A novel SiO2 supported Pd metal catalyst for the Heck reaction

A ligand-free heterogeneous metal catalyst system (represented as Pd/SiO₂ (O)) derived by calcination of Pd(acac)₂/SiO₂ in air and its catalytic properties toward the Heck coupling of bromobenzene (PhBr) and styrene have been studied. X-ray photoelectron spectroscopy (XPS) and catalytic results demonstrate that most of Pd²⁺ is reduced to Pd⁰ on SiO₂ by N,N-dimethylacetamide (DMA) during the Heck reaction and that the resulting Pd⁰/SiO₂ is highly active for the Heck reaction, the remaining Pd²⁺/SiO₂ is not responsible for the high activity. Pd/SiO₂ (O) possesses incomparable advantages over a heterogeneous homolog (represented as Pd/SiO₂ (H)) prepared by reduction of Pd(acac)₂/SiO₂ in H₂ as a pre-catalyst in both activity and catalyst recycling. The activity over Pd/SiO₂ (O) is comparable to that over a homogeneous Pd system. Transmission electron microscopy (TEM) analysis illustrates that the high activity over Pd/SiO₂ (O) consists in the small size of supported Pd particles generated in-situ with gentle reducing agents at a mild temperature.     

Performances of Pd Nanoparticles on Different Supports in the Direct Synthesis of H2O2 in CO2-Expanded Methanol

Catalysts based on Pd supported on SiO₂, SBA-15, ??-Al₂O₃ and N-CNT were investigated for the direct H₂O₂ synthesis and decomposition/hydrogenolysis in CO₂-expanded methanol in batch and semi-batch reactors working at room temperature and a pressure of 6.5 bar. The order of reactivity for the synthesis of H₂O₂ per g of Pd or for the rate of H₂O₂ decomposition, or the selectivity to H₂O₂ does not correlate with the acidity of the support. A relation was observed with the Pd particle sizes, i.e. smaller particles lead to a higher specific activity, but the sample supported on carbon nanotube shows an order of magnitude higher specific activity per g of Pd, indicating the presence of an additional factor attributed to the interaction with the carbon support which determines an intrinsic higher reactivity. However, this higher reactivity corresponds also to a higher activity in the consecutive conversion of H₂O₂, probably by hydrogenolysis reaction. A rough relation between activity in H₂O₂ synthesis and in H₂O₂ conversion was observed in the samples with the different supports, indicating the similar nature of the active sites responsible for the two reactions. Finally, the analysis of the recyclability of the catalysts and transmission electron microscopy (TEM) characterization data after the catalytic tests indicate that the use of CO₂-expanded methanol allows improving the catalytic performances in H₂O₂ direct synthesis due to the enhanced solubility of H₂ and O₂, but induces a fast catalyst deactivation due to an enhanced mobility and sintering of the supported Pd particles. The effect is present in all the four type of support used.     

Production of middle distillate through hydrocracking of paraffin wax over Pd/SiO2–Al2O3 catalysts

Pd/SiO₂–Al₂O₃ catalysts (Pd/SA-X) with different SiO₂ contents (X, wt%) were prepared for use in the production of middle distillate (C₁₀–C₂₀) through hydrocracking of paraffin wax. The effect of SiO₂ content of Pd/SA-X catalysts on their physicochemical properties and catalytic performance in the hydrocracking of paraffin wax was investigated. High surface area and well-developed mesopores of Pd/SA-X catalysts improved the dispersion of Pd species on the SiO₂–Al₂O₃ support. Acidity of Pd/SA-X catalysts determined by NH₃-TPD experiments showed a volcano-shaped trend with respect to SiO₂ content. Conversion of paraffin wax increased with increasing acidity of the catalyst, while selectivity for middle distillate decreased with increasing acidity of the catalyst. Yield for middle distillate showed a volcano-shaped curve with respect to acidity of the catalyst. This indicates that acidity of Pd/SA-X catalysts played an important role in determining the catalytic performance in the hydrocraking of paraffin wax. Among the catalyst tested, Pd/SA-69 with moderate acidity showed the highest yield for middle distillate.     

Direct formation of H2O2 from H2 and O2 and decomposition/hydrogenation of H2O2 in aqueous acidic reaction medium over halide-containing Pd/SiO2 catalytic system

Formation of H₂O₂ from H₂ and O₂ and decomposition/hydrogenation of H₂O₂ have been studied in aqueous acidic medium over Pd/SiO₂ catalyst in presence of different halide ions (viz. F⁻, Cl⁻ and Br⁻). The halide ions were introduced in the catalytic system via incorporating them in the catalyst or by adding into the reaction medium. The nature of the halide ions present in the catalytic system showed profound influence on the H₂O₂ formation selectivity in the H₂ to H₂O₂ oxidation over the catalyst. The H₂O₂ destruction via catalytic decomposition and by hydrogenation (in presence of hydrogen) was also found to be strongly dependent upon the nature of the halide ions present in the catalytic system. Among the different halides, Br⁻ was found to selectivity promote the conversion of H₂ to H₂O₂ by significantly reducing the H₂O₂ decomposition and hydrogenation over the catalyst. The other halides, on the other hand, showed a negative influence on the H₂O₂ formation by promoting the H₂ combustion to water and/or by increasing the rate of decomposition/hydrogenation of H₂O₂ over the catalyst. An optimum concentration of Br⁻ ions in the reaction medium or in the catalyst was found to be crucial for obtaining the higher H₂O₂ yield in the direct synthesis.     

Influence of nature/concentration of halide promoters and oxidation state on the direct oxidation of H2 to H2O2 over Pd/ZrO2 catalysts in aqueous acidic medium

The nature/concentration of halide promoters and influence of the Pd oxidation state on the promoted reaction system has been investigated on the direct H₂O₂ process over a 2.5 wt.% Pd/ZrO₂ catalyst in an aqueous acidic reaction medium. The oxidation state of Pd had a profound influence on the H₂O₂ synthesis process. Interestingly, the nature of the halide determined the magnitude/type of influence the Pd oxidation state exerted on the overall process. While the effect of the oxidation state on the H₂O₂ yields was large for the reaction systems containing F⁻ or no halide, the effect was significantly smaller for the reaction systems containing Br⁻ and Cl⁻. The nature of the halide also strongly influenced the H₂O₂ synthesis process. Br⁻ strongly enhanced the H₂O₂ yields, while F⁻ had a negative influence on the H₂O₂ yields. The ability of the halides to enhance the H₂O₂ process was found to strongly depend on its propensity to suppress the secondary H₂O₂ decomposition reaction. The influence of Br⁻ and Cl⁻concentration studies revealed that the optimum halide concentration for the direct H₂O₂ synthesis process was dependent on the nature of the halide. While the maximum in H₂O₂ yields for the Br⁻ containing reaction medium corresponded to a concentration of ∼0.9 mmol/dm³ (KBr) the maximum for the Cl⁻ containing solution was obtained at ∼1.5 mmol/dm³ (KCl). Such knowledge is crucial from the viewpoint of optimization (catalyst/reaction system screening studies) of the direct H₂O₂ process. The qualitative trends (H₂O₂ selectivity/yield) observed in case of the incorporated halide catalysts were similar to those observed with halides in reaction medium over the Pd/ZrO₂ catalyst.     

Hydrogenation of 2-Ethylanthraquinone over Pd/SiO2 and Pd/Al2O3 in the Fixed-Bed Reactor. The Effect of the Type of Support

The effects of the type of support and Pd concentration profile in alumina and silica supported egg-shell catalysts and their performance in the hydrogenation of 2-ethylanthraquinone (eAQ) were studied in 'Anthra' (AQ) and 'All-Tetra' systems. The activity and deactivation of catalysts were determined in the fixed-bed reactor. Solution saturated with hydrogen, (concentration of active quinones 60g/dm³, eAQ in the AQ system, 30% of eAQ and 70% of H₄eAQ–2-ethlytetrahydroanthraquinone, in the All-Tetra system) was circulated through the catalyst bed at temperature 50°C and pressure 5bar. The contents of eAQ, active quinones, H₄eAQ and degradation products were determined in the course of hydrogenation by GC method. The egg-shell palladium catalysts (1–2wt% Pd) prepared by the precipitation of palladium hydroxide onto alumina and silica supports pre-impregnated with various alkaline (NaHCO₃, NaH₂PO₄, Na₂SiO₃) solutions were used in the hydrogenation experiments. Pd concentration profile inside the grains of catalysts was characterized by scanning electron microscopy. A difference between alumina and silica carriers with respect to the course of side reactions producing degradation products was found. Degradation of quinones in the hydrogenolytic reactions predominated on alumina supported catalysts, while the catalysts with silica favoured the hydrogenation of aromatic rings resulting in H₄eAQ-active quinone. As a crucial factor for the decrease in the activity during the hydrogenation run, the reactivity of catalyst in the hydrogenolytic reactions was established. Alumina supported catalysts exhibited much higher deactivation than those of silica supported ones. Silica carrier as well as silica species introduced onto alumina under pre-impregnation with Na₂SiO₃ exhibited an advantageous role in the catalyst performance, in terms of activity and deactivation.     

Highly dispersed carbon-supported Pd nanoparticles catalyst synthesized by novel precipitation–reduction method for formic acid electrooxidation

The highly dispersed and ultrafine carbon-supported Pd nanoparticles (Pd/C) catalyst is synthesized by using an improved precipitation–reduction method, which involves in Pd^II → PdO·H₂O → Pd⁰ reaction path. In the method, palladium oxide hydrate (PdO·H₂O) nanoparticles (NPs) with high dispersion is obtained easily by adjusting solution pH in the presence of 1,4-butylenediphosphonic acid (H₂O₃P-(CH₂)₄-PO₃H₂, BDPA). After NaBH₄ reduction, the resulting Pd/C catalyst possesses high dispersion and small particle size. As a result, the electrochemical measurements indicate that the resulting Pd/C catalyst exhibits significantly high electrochemical active surface area and high electrocatalytic performance for formic acid electrooxidation compared with that prepared by general NaBH₄ reduction method.     

Palladium Catalysts for Fatty Acid Deoxygenation: Influence of the Support and Fatty Acid Chain Length on Decarboxylation Kinetics

Supported metal catalysts containing 5?wt% Pd on silica, alumina, and activated carbon were evaluated for liquid-phase deoxygenation of stearic (octadecanoic), lauric (dodecanoic), and capric (decanoic) acids under 5?% H₂ at 300?°C and 15?atm. On-line quadrupole mass spectrometry (QMS) was used to measure CO?+?CO₂ yield, CO₂ selectivity, H₂ consumption, and initial decarboxylation rate. Post-reaction analysis of liquid products by gas chromatography was used to determine n-alkane yields. The Pd/C catalyst was highly active and selective for stearic acid (SA) decarboxylation under these conditions. In contrast, SA deoxygenation over Pd/SiO₂ occurred primarily via decarbonylation and at a much slower rate. Pd/Al₂O₃ exhibited high initial SA decarboxylation activity but deactivated under the test conditions. Similar CO₂ selectivity patterns among the catalysts were observed for deoxygenation of lauric and capric acids; however, the initial decarboxylation rates tended to be lower for these substrates. The influence of alkyl chain length on deoxygenation kinetics was investigated for a homologous series of C₁₀?CC₁₈ fatty acids using the Pd/C catalyst. As fatty acid carbon number decreases, reaction time and H₂ consumption increase, and CO₂ selectivity and initial decarboxylation rate decrease. The increase in initial decarboxylation rates for longer chain fatty acids is attributed to their greater propensity for adsorption on the activated carbon support.     

Methanol synthesis over Pd/SiO2 with narrow Pd size distribution prepared by using MCM-41 as a support precursor

All silicious MCM-41 was investigated as a support or a support precursor for Pd/SiO₂ and prepared catalysts were tested for methanol synthesis from CO and H₂. The methods of Pd loading on the MCM-41 were impregnation, seed impregnation and chemical vapor deposition (CVD). For both impregnations, most Pd existed outside of the pore as large particles, and only a small part of Pd was inserted into the pore of MCM-41 retaining the initial structure. On the contrary, in the catalyst prepared by CVD method, the MCM-41 structure was completely destroyed to become amorphous SiO₂. Yet the average Pd particle size in this catalyst was smaller and its distribution was narrower than those of the catalysts prepared by impregnation methods. In the methanol synthesis from CO hydrogenation the catalyst prepared by CVD showed higher methanol selectivity than other MCM-41-derived catalysts. This result was considered to be due to the more uniform distribution of the Pd particle size.     

Catalytic dehydrogenation of propane on chromia,palladium and platinum supported catalysts

The dehydrogenation of propane to propylene over Cr₂O₃/Al₂O₃, Pd/Al₂O₃ and Pt/SiO₂ has been investigated in the temperature range 580–618°C. Runs were performed on propane, alone or in the presence of nitrogen (as a diluent), with complete analysis of the reaction products. The reaction was carried out in a fixed bed reactor at space velocities from 450–800 h^?1 which are close to industrial values and at pressures from 0.3 to 1 atm. A set of runs was made over a commercial chromia-alumina catalyst (10% Cr₂O₃) and over a promoted catalyst prepared in the laboratory by impregnation (16.8% Cr₂O₃ + 2% K₂O). The latter catalyst showed high selectivity and stability even when subjected to continuous cycles of dehydrogenation, regeneration and purging. Of the two noble metal supported catalysts used, reduced Pd/Al₂O₃ showed higher activity than Pt/SiO₂ at 618°C. The former catalyst gave a propylene yield of around 98% at 20% conversion level.     

Reactivity Aspects of SBA15-Based Doped Supported Catalysts: H2O2 Direct Synthesis and Disproportionation Reactions

Pd and PdAu catalysts supported on SBA15 and SiO₂ were prepared and investigated for H₂O₂ direct synthesis in a batch autoclave (10 °C and 17.5 bar) and in the absence of halides and acids. The SiO₂ supported catalysts exhibited inferior performances compared to the mesoporous ordered SBA15. A good control of both the catalysts dispersion and nanoparticle stability was achieved using SBA15. Catalysts were doped with bromine, a promoter in the H₂O₂ direct synthesis. Productivity and selectivity decreased when bromine was incorporated in the catalysts, thus indicating a possible poisoning due to the grafting process. A synergetic effect between Pd and Au was observed both in presence and absence of bromopropylsilane grafting on the catalyst surface. Three modifiers of the SBA15 support (Al, CeO₂ and Ti) were chosen to elucidate the influence of the surface properties on metal dispersion and catalytic performance. Higher productivity and selectivity were achieved incorporating Al into the SBA15 framework, whereas neither Ti nor CeO₂ improved H₂O₂ yields. The enhanced performance observed for the Prau/Al–SBA15 catalysts was attributed to the increased number of Brønsted acid sites. A modification of this catalyst with bromine was confirmed to impair both productivity and selectivity, possibly due to the broader particle size distribution and the poor stability of the metal nanoparticles, as demonstrate by transmission electron microscopy (TEM) images. H₂O₂ disproportionation was also investigated. A much slower reaction rate was observed compared to the H₂O₂ production, suggesting that the major contributor in the process of H₂O₂ destruction must be connected to the hydrogenation reaction.