Direct synthesis of hydrogen peroxide from hydrogen and oxygen over a Pd core-silica shell catalyst

Pd core–silica shell particles (Pd@SiO₂) were prepared by encapsulating Pd colloids with a silica shell through the Stöber method. The palladium core particles were well dispersed (Dispersion = 43%) and had uniform size (4 nm) and shape inside the porous silica shell. Pd@SiO₂ showed good catalytic activity (554 mmol H₂O₂/g Pd·h) for the direct synthesis of H₂O₂, which was better than those of impregnated Pd catalysts (Pd/SiO₂ and Pd/Al₂O₃). It is expected that the stabilization of less coordinated Pd crystals in a highly dispersed state by core-shell formation is effective for the improvement of H₂O₂ production.     

氢氧直接合成过氧化氢贵金属催化剂的研究

采用浸渍法制备了一系列负载型钯催化剂，用于催化氢气和氧气直接合成过氧化氢的反应。分别考察了钯负载节、溶剂、载体预处理对反应的影响；结合XPS分析推断了催化剂活性组分价态。结果发现钯最佳负载量为1．88％（质量分数）；氢气在溶剂中的溶解度越大其反应转化率也越高，其中甲醇和丙酮都是良好的溶剂；载体经过卤化铵预处理可大幅度地提高催化剂的选择性；金属态钯为具有催化活性的价态。     

Direct synthesis of hydrogen peroxide from H2/O2 and oxidation of thiophene over supported gold catalysts

Direct synthesis of hydrogen peroxide from H₂ and O₂ was performed over supported gold catalysts. The catalysts were characterized by means of UV–vis, H₂-TPR, TEM and XPS. Based on the results we conclude that metallic Au is the active species in the direct synthesis of hydrogen peroxide from H₂ and O₂. During preparation process of catalyst by deposition–precipitation with urea, the pH value increased and the gold particle size decreased with increasing the urea concentration. The catalyst prepared with higher urea concentration showed a higher activity and its stability also was efficiently improved. Gold nanoparticles, supported on TiO₂ or Ti contained supports, gave a higher catalytic activity. Thiophene can be efficiently oxidized by hydrogen peroxide synthesized in situ from H₂ and O₂ over Au/TS-1.     

氢氧直接合成过氧化氢用催化剂的研究进展

过氧化氢（H₂O₂）是一种高效的绿色氧化剂,广泛应用于化学品合成、印染纺织、污水处理等领域。近年来,氢氧直接合成过氧化氢作为一种简单、环保、原子效率高的合成方法,成为一大研究热点。本文系统性地介绍了近年来氢氧直接合成过氧化氢催化剂的催化反应机理,负载金属的不同结构和性质对直接合成过氧化氢的催化性能与作用机理,重点讨论了与催化剂载体相关的载体结构、载体酸性、载体添加物、载体与金属相互作用等方面对反应活性和选择性的影响。最后对比了近年来直接合成过氧化氢用催化剂的催化性能,认为合成高选择性、高产率的催化剂仍是未来直接合成过氧化氢工业化应用的发展方向。     

Direct production of hydrogen peroxide from oxygen and hydrogen applying membrane-permeation mechanism

Direct synthesis of hydrogen peroxide is conducted using a palladium membrane reactor. The palladium membrane is prepared on the external surface of the porous α-alumina tubing, by electroless plating (ELP) or chemical vapor deposition (CVD). Thus prepared membrane is immersed into aqueous reaction solution. Hydrogen is supplied from inside of the palladium membrane, while oxygen was bubbled in the reaction solution. Both reacted at the surface of the membrane to produce hydrogen peroxide. Hydrogen peroxide is produced steadily for more than 80 h and the selectivity based on the amount of reacted hydrogen was estimated to be ca. 50%. The reactor performance is investigated in correlation with membrane properties and the hydrogen/oxygen supply pressures.     

Direct synthesis of hydrogen peroxide from hydrogen and oxygen: An overview of recent developments in the process

Hydrogen peroxide (H₂O₂) is an important commodity chemical and its demand is growing significantly in the chemical synthesis due to its “green” character. Currently, H₂O₂ is produced almost exclusively by the anthraquinone auto-oxidation (AO) process. The AO process involves indirect oxidation of hydrogen and thus avoids potentially explosive H₂/O₂ mixture. However, this large-scale process presents significant safety issues associated with the transport of bulk H₂O₂. Moreover, the AO process can hardly be considered an environmentally friendly method. In view of this, more economical and environmentally cleaner routes have been explored for the production of H₂O₂. The liquid-phase catalytic direct synthesis of H₂O₂ from H₂ and O₂ offers an attractive green technology for small-scale/on-site production of H₂O₂. However, the direct synthesis process suffers from two major drawbacks: (i) potential hazards associated with H₂/O₂ mixtures and (ii) poor selectivity for H₂O₂ because the catalysts used for H₂O₂ synthesis are also active for its decomposition and hydrogenation to water as well as for H₂ combustion. These serious issues and the recent developments in the direct H₂O₂ synthesis are discussed in this review. The roles of protons (H⁺) and halide ions in promoting the H₂O₂ selectivity are also examined in detail.     

氢氧直接合成过氧化氢技术的工业化概况

简单介绍了氢氧直接合成过氧化氢(DSHP)技术的优缺点,结合有关专利分别详细介绍了杜邦公司和Evonik–Headwaters公司的DSHP工艺。最后指出,DSHP是一种值得广泛而深入进行研究和开发的、代表过氧化氢合成工艺未来发展方向的绿色合成工艺。     

Direct synthesis of hydrogen peroxide from H2 and O2 and in situ oxidation using zeolite-supported catalysts

Four microporous materials, zeolites HZSM-5, Y, Beta and TS-1, were used as the supports to prepare supported gold catalysts using impregnation or deposition precipitation. The gold catalysts were tested in the direct synthesis of hydrogen peroxide from H₂ and O₂ and for CO oxidation. The effect on the catalytic activity of different metal (e.g., Pd, Pt, Cu, Ag, Rh or Ru) on the synthesis of hydrogen peroxide was also tested. Organic substrates, such as cyclohexane or cyclooctene, were introduced to investigate the possibility of in situ H₂O₂ oxidation with these catalysts.     

Direct epoxidation of propylene with hydrogen peroxide over TS-1 catalysts: Effect of hydrophobicity of the catalysts

TS-1 (titanium silicalite-1) catalysts were hydrothermally synthesized in the presence of polymethylmethacrylate bead (denoted as TS-1_PMMA) and polystyrene bead (denoted as TS-1_PS) for use in the direct epoxidation of propylene with hydrogen peroxide. TS-1 catalyst was also synthesized by a hydrothermal method in the absence of polymer bead. It was revealed that TS-1_PMMA and TS-1_PS catalysts showed a better catalytic performance than TS-1 catalyst in terms of conversion of hydrogen peroxide, selectivity for propylene oxide, and yield for propylene oxide, due to their enhanced hydrophobicity. Among three catalysts, TS-1_PS with the highest hydrophobicity showed the best catalytic performance.     

Direct synthesis of phenol from benzene over hydroxyapatite catalysts

The direct synthesis of phenol from benzene in the gas phase was studied over hydroxyapatite catalysts. The reaction was carried out in a fixed-bed reactor at atmospheric pressure and reaction temperature of 450°C in the presence of ammonia. A high selectivity (about 97%) of phenol formation at about 3.5% conversion of benzene was achieved over catalysts containing Ca and Cu ions in the cation part of hydroxyapatite. Besides phenol as the main reaction product, aniline is also formed. The reaction mechanism involves formation of N₂O from NH₃ in the first step of reaction. Benzene is oxidized by active oxygen species which are formed on the catalyst by decomposition of N₂O.     

用氢氧的非平衡等离子体直接合成过氧化氢

引言 过氧化氢是一种多用途绿色氧化剂,目前主要用蒽醌法生产.蒽醌法虽然技术成熟,但过程复杂,装置投资大,生产成本高,且对环境有污染.因此,近年来国外对于以氢气和氧气为原料,直接合成过氧化氢的新方法研究十分重视[1-3].     

Direct synthesis of hydrogen peroxide over Pd nanoparticles embedded between HZSM-5 nanosheets layers

Direct synthesis of hydrogen peroxide (DSHP) was studied over Pd loaded on HZSM-5 nanosheets (Pd/ZN). Pd nanoparticles with average size of ca. 4.3 nm were introduced into the adjacent nanosheet layers (thickness of ca. 2.9 nm) by impregnation method. Pd/ZN with theoretical Si/Al molar ratio of 25 showed the highest selectivity for H₂O₂ among the prepared catalysts, together with highest formation rate of H₂O₂ (38.0 mmol·(g cat)^-1·h^-1), 1.9 times than that of Pd supported on conventional HZSM-5 zeolite (Pd/CZ-50). Better catalytic performance of nanosheet catalysts was attributed to the promoted Pd dispersion which promoted H₂ dissociation, more Brønsted acid sites and stronger metal-support interaction which inhibited the dissociation of O-O bond in H₂O₂. The embedded structure sufficiently protected the Pd nanoparticles by space confinement which restrained the Pd leaching, leading to a better catalytic stability with 90% activity retained after 3 cycles, which was almost 3 times than that of Pd/CZ-50 (30.4% activity retained).     

Direct synthesis of hydrogen peroxide over Pd nanoparticles embedded between HZSM-5 nanosheets layers

Direct synthesis of hydrogen peroxide (DSHP) was studied over Pd loaded on HZSM-5 nanosheets (Pd/ZN). Pd nanoparticles with average size of ca. 4.3 nm were introduced into the adjacent nanosheet layers (thickness of ca. 2.9 nm) by impregnation method. Pd/ZN with theoretical Si/Al molar ratio of 25 showed the highest selectivity for H₂O₂ among the prepared catalysts, together with highest formation rate of H₂O₂ (38.0 mmol·(g cat)⁻¹·h⁻¹), 1.9 times than that of Pd supported on conventional HZSM-5 zeolite (Pd/CZ-50). Better catalytic performance of nanosheet catalysts was attributed to the promoted Pd dispersion which promoted H₂ dissociation, more Brønsted acid sites and stronger metal-support interaction which inhibited the dissociation of OO bond in H₂O₂. The embedded structure sufficiently protected the Pd nanoparticles by space confinement which restrained the Pd leaching, leading to a better catalytic stability with 90% activity retained after 3 cycles, which was almost 3 times than that of Pd/CZ-50 (30.4% activity retained).     

反应介质对氢氧直接合成过氧化氢的影响研究

以超声浸渍法制备的PdO／γ-Al2O3-U为催化剂,考察不同无机酸、不同硫酸浓度对氢氧直接合成过氧化氢的影响。结果表明：酸性介质有利于氢氧直接合成过氧化氢,当反应介质为H2SO4溶液时,氢氧直接合成过氧化氢收率好于其他,其最佳浓度为0．35mol／L。     

由氢与氧直接合成过氧化氢研发新进展

综述了2016年以来国内外由氢与氧直接合成过氧化氢的研发进展,其中主要包括所用催化剂性能提高、合成装置和方法改进以及合成反应机理。介绍了多种不同催化金属(仍以Pd为主)、不同载体的催化剂和催化金属纳米颗粒(簇)形态及粒径、载体多种选择等对提高催化性能尤其是生成过氧化氢选择性的影响,以期获得更理想的催化剂。简要介绍了不同形式反应器和不同反应条件对反应结果尤其是反应选择性的影响。最后介绍了一些学者对直接合成过氧化氢过程中化学反应途径和机理所进行的较为详细和深入的研究以及所取得的结果和新发现。     

Epoxidation of propylene and direct synthesis of hydrogen peroxide by hydrogen and oxygen

The autoreduction of palladium–platinum-containing titanium silicalite leads to an effective catalyst for the epoxidation of propylene to propylene oxide by O₂ in the presence of H₂. The one-pot reaction is favoured compared to the two-step reaction path.     

Direct synthesis of hydrogen peroxide from H2 and O2 using zeolite-supported Au-Pd catalysts

The direct synthesis of hydrogen peroxide from H₂ and O₂ using zeolite-supported Au-Pd catalysts is described using two zeolites, ZSM-5 and zeolite Y, using an impregnation method of preparation. The addition of Pd to Au for these catalysts significantly enhances the productivity for hydrogen peroxide. The use of zeolites as a support for Au-Pd gives higher rates of hydrogen peroxide formation when compared with alumina-supported Au catalysts prepared using a similar method. The addition of metals other than Pd is also investigated, but generally Au-Pd catalysts give the highest activity for the synthesis of hydrogen peroxide. The addition of Ru and Rh have no significant effect, but the addition of Pt does enhance the activity for the selective formation of hydrogen peroxide.     

Direct synthesis of hydrogen peroxide from H2 and O2 using zeolite-supported Au catalysts

The direct synthesis of hydrogen peroxide from H₂ and O₂ using zeolite-supported Au catalysts is described and their activity is contrasted with silica- and alumina-supported Au catalysts. Two zeolites were investigated, ZSM-5 and zeolite Y. The effect of calcination of these catalysts is studied and it is found that for uncalcined catalysts high rates of hydrogen peroxide formation are observed, but these catalysts are unstable and lose Au during use. Consequently, reuse of these catalysts leads to lower rates of hydrogen peroxide formation. However, catalysts calcined at 400 °C are more stable and can be reused without loss of gold. The use of zeolites as a support for Au gives comparable rates of hydrogen peroxide formation to alumina-supported Au catalysts and higher rates when compared with silica-supported catalysts. prepared using a similar method. Zeolite Y-supported catalysts are more active than ZSM-5-supported catalysts for the stable calcined materials. It is considered that the overall activity of these supported catalysts may be related to the aluminium content as the activity increases with increasing aluminium content.     

Catalytic synthesis of methanethiol from hydrogen sulfide and carbon monoxide over vanadium-based catalysts

The direct synthesis of methanethiol, CH₃SH, from CO and H₂S was investigated using sulfided vanadium catalysts based on TiO₂ and Al₂O₃. These catalysts yield high activity and selectivity to methanethiol at an optimized temperature of 615 K. Carbonyl sulfide and hydrogen are predominant products below 615 K, whereas above this temperature methane becomes the preferred product. Methanethiol is formed by hydrogenation of COS, via surface thioformic acid and methylthiolate intermediates. Water produced in this reaction step is rapidly converted into CO₂ and H₂S by COS hydrolysis.

Titania was found to be a good catalyst for methanethiol formation. The effect of vanadium addition was to increase CO and H₂S conversion at the expense of methanethiol selectivity. High activities and selectivities to methanethiol were obtained using a sulfided vanadium catalyst supported on Al₂O₃. The TiO₂, V₂O₅/TiO₂ and V₂O₅/Al₂O₃ catalysts have been characterized by temperature programmed sulfidation (TPS). TPS profiles suggest a role of V₂O₅ in the sulfur exchange reactions taking place in the reaction network of H₂S and CO.     

The role of hydrogen in methanol synthesis over copper catalysts

The experimental observation that the activity of a series of zinc oxide supported copper catalysts is related to the surface area of the copper is examined in the light of recent evidence that hydrogen spillover from copper to zinc oxide is facile. A model is proposed which explains the effect of zinc oxide on copper in terms of a reversible transfer of hydrogen between copper and zinc oxide. It is suggested that therate determining step normally occurs on the surface of the copper but that therate of reaction can be dependent on the availability of spillover hydrogen from the zinc oxide.