Factors influencing decomposition of H2O2 over supported Pd catalyst in aqueous medium

Since H₂O₂ decomposition can result in selectivity/yield loss in the direct H₂O₂ synthesis process from H₂ and O₂ over supported Pd catalysts, it is important to have an enhanced understanding about the factors affecting the H₂O₂ decomposition reaction. Herein, detailed studies have been undertaken to investigate the influence of different factors, such as (a) nature and concentration of acid in reaction medium, (b) nature and concentration of halide in presence and absence of acid in reaction medium, (c) pretreatment procedures and (d) catalyst modification by incorporation of different halides, on the H₂O₂ decomposition reaction over a 5% Pd/C catalyst in aqueous medium at 25 °C. This study has shown that the H₂O₂ decomposition activity is profoundly influenced by all the above factors. The effectiveness of the acids in suppressing the H₂O₂ decomposition activity decreased in the following order: hydroiodic acid > hydrobromic acid > hydrochloric acid  acetic acid > phosphoric acid > sulfuric acid > perchloric acid. The ability of the acid to decrease the H₂O₂ decomposition activity was found to very strongly depend on the nature of its associated anion. Halides, such as iodide, bromide and chloride were particularly effective in suppressing the H₂O₂ decomposition activity. Oxidation pretreatment of the catalyst was found to strongly suppress its H₂O₂ decomposition activity, while a reduction treatment was found to promote its activity. A gradual decrease in the H₂O₂ decomposition activity of the catalyst was observed with each successive usage due to in situ sub-surface oxidation of Pd by H₂O₂. Halide incorporation either via the reaction medium or prior catalyst modification had a similar qualitative effect on the H₂O₂ decomposition activity.     

光催化氧气还原制备H2O2

H2O2广泛应用于化工和环保领域,其分解的唯一产物是水,有利于生产与自然生态系统的协调可持续发展.工业上H2O2的合成主要是通过蒽醌法间接合成,该方法能耗大,污染环境.而直接由H2与O2混合制备H2O2,具有极大的安全风险,且需要消耗大量H2.通过光催化技术将O2和H2O转化成H2O2的方法,避免了H2与O2的直接混合...     

Catalytic decomposition of H2O2 on Co3O4 doped with MgO and V2O5

The effects of doping of Co₃O₄with MgO (0.4–6 mol%) and V₂O₅ (0.20–0.75 mol%) on its surface and catalytic properties were investigated using nitrogen adsorption at −196°C and decomposition of H₂O₂ at 30–50°C. Pure and doped samples were prepared by thermal decomposition in air at 500–900°C, of pure basic cobalt carbonate and basic carbonate treated with different proportions of magnesium nitrate and ammonium vanadate. The results revealed that, V₂O₅ doping followed by precalcination at 500–900°C did not much modify the specific surface area of the treated Co₃O₄ solid. Treatment of Co₃O₄ with MgO at 500–900°C resulted in a significant increase in the specific surface area of cobaltic oxide. The catalytic activity in H₂O₂ decomposition, of Co₃O₄ was found to suffer a considerable increase by treatment with MgO. The maximum increase in the catalytic reaction rate constant (k) measured at 40°C on Co₃O₄ due to doping with 3 mol% MgO attained 218, 590 and 275% for the catalysts precalcined at 500, 700 and 900°C, respectively. V₂O₅-doping of Co₃O₄ brought about a significant progressive decrease in its catalytic activity. The maximum decrease in the reaction rate constant measured at 40°C over the 0.75 mol% V₂O₅-doped Co₃O₄ solid attained 68 and 93% for the catalyst samples precalcined at 500 and 900°C, respectively. The doping process did not modify the activation energy of the catalyzed reaction but much modified the concentration of catalytically active constituents without changing their energetic nature. MgO-doping increased the concentration of CO³⁺–CO²⁺ ion pairs and created Mg²⁺–CO³⁺ ion pairs increasing thus the number of active constituents involved in the catalytic decomposition of H₂O₂. V₂O₅-doping exerted an opposite effect via decreasing the number of CO³⁺–CO²⁺ ion pairs besides the possible formation of cobalt vanadate.     

MOF derived Co3O4/N-doped carbon nanotubes hybrids as efficient catalysts for sensitive detection of H2O2 and glucose

Developing enzyme-free sensors with high sensitivity and selectivity for H2O2 and glucose is highly desirable for biological science.Especially,it is attractive to exploit noble-metal-free nanomaterials with large surface area and good conductivity as highly active and selective catalysts for molecular detection in enzyme-free sensors.Herein,we successfully fabricate hollow frameworks of Co3O4/N-doped carbon nanotubes(Co3O4/NCNTs)hybrids by the pyrolysis of metal-organic frameworks followed by calcination in the air.The as-prepared novel hollow Co3O4/NCNTs hybrids exhibit excellent electrochemical performance for H2O2 reduction in neutral solutions and glucose oxidation in alkaline solutions.As sensor electrode,the Co3O4/NCNTs show excellent non-enzymatic sensing ability towards H2O2 response with a sensitivity of 87.40μA(mmol/L)^-1 cm^-2,a linear range of 5.00μmol/L-11.00 mmol/L,and a detection limitation of 1μmol/L in H2O2 detection,and a good glucose detection performance with 5μmol/L.These excellent electrochemical performances endow the hollow Co3O4/NCNTs as promising alternative to enzymes in the biological applications.     

超临界水热极速合成异质结构H4SiW12O40/Bi2WO6光催化剂及其脱氮性能

采用超临界水热合成方式极速合成一种H_4SiW_(12)O_(40)/Bi_2WO_6光催化剂,通过X射线衍射(XRD)、场发射扫描电子显微镜(SEM)、透射电子显微镜(TEM)、比表面积及孔隙度(BET)测定对所合成催化剂的结构和性质进行了考察,并以吡啶含量为15 mg/g的模拟油对光催化剂的脱氮效果进行评价。结果表明,该光催化剂为二维纳米片自组装成的三维球状结构,其中,H_4SiW_(12)O_(40)与Bi_2WO_6不是简单的固载关系而是在超临界水热条件下生成一种新的晶相,正是由于这种晶相的存在,使得H_4SiW_(12)O_(40)牢固固载在Bi_2WO_6光催化剂本体上的同时,对光生载流子进行了有效疏导,提升了H_4SiW_(12)O_(40)/Bi_2WO_6光催化剂的使用寿命和光催化活性。本研究针对光催化剂制备周期与晶形发育的矛盾,将超临界水热技术与光催化剂模板导向合成技术有机结合,在获得良好晶形异质结构H_4SiW_(12)O_(40)/Bi_2WO_6光催化剂的同时明显缩短了光催化剂的制备周期,从而降低了催化剂的制备成本,攻克了光催化剂工业化应用的主要矛盾,所制备的H_4SiW_(12)O_(40)/Bi_2WO_6光催化剂轻质油脱氮效率达97%以上。     

Mg-Al LDH的制备及Mg-Al LDH/H2O2体系降解水中环丙沙星的研究

分别以MgO和Al(OH)3为镁源及铝源,采用水热法制备Mg-Al LDH,研究了水热温度和氢氧化钠浓度对水热产物纯度的影响。结果显示在NaOH/MgO/Al(OH)3/(Na₂CO₃)摩尔比为2∶1∶0.5∶0.25,水热反应温度在120~150℃,反应12 h,可以得到纯相Mg-Al LDH。进一步以所制备的Mg-Al LDH为吸附剂,H₂O₂为氧化剂。系统研究了Mg-Al LDH/H₂O₂体系溶液pH、H₂O₂用量、污染物浓度、反应温度、反应时间等因素对Mg-Al LDH/H₂O₂体系降解水体中环丙沙星效果的影响。当Mg-Al LDH用量为0.05 g,H₂O₂用量为2 mL,系统pH为6.98,反应温度为35℃,环丙沙星浓度为30 mg·L^-1时,反应13 min环丙沙星的降解率可达97%。随着反应温度的升高,反应速率及平衡时降解率均有所提高,该过程可以用拟一级动力学方程描述,反应的表观活化能E a为19.29 kJ·mol^-1,指前因子A为0.38×10³ min^-1。Mg-Al LDHs/H₂O₂体系降解环丙沙星过程受反应速率控制,而非受传质控制。     

SiO_2负载磷钨钒杂多酸杂化材料的制备及其氧化脱硫性能的研究

利用磷酸氢二钠、偏钒酸纳和钨酸钠为原料,合成了具有Keggin结构的磷钨钒杂多化合物(H5PW10V2O40),并与1-丁基-3-甲基咪唑溴(BmimBr)离子液体反应生成一种杂多酸杂化材料([Bmim]5PW10V2O40)。利用红外光谱(FT-IR)、X射线衍射光谱(XRD)和紫外可见光谱(UV-vis)对所合成的杂多酸杂化材料进行表征。结果表明,[Bmim]5PW10V2O40具有咪唑阳离子基团和Keggin型杂多阴离子基团的结构特征,并且两种基团之间存在相互作用。以SiO_2为载体制备负载型的杂多酸杂化材料催化剂[Bmim]5PW10V2O40/SiO_2,以H2O_2作为氧化剂,考察该催化剂对模拟油中DBT的氧化性能,并优化氧化反应条件,在反应温度40℃,O/S物质的量比为3.0的条件下,反应50min,模拟油品中的DBT的转化率可以达到100%。催化剂可以通过离心法分离,经过干燥之后,可以循环使用至少七次,而对DBT的氧化活性没有降低。     

Fe2O3/Al2O3氧载体用于甲烷化学链燃烧：负载量与制备方法的影响

以不同方法制备了系列Fe₂O₃/Al₂O₃氧载体,采用XRD、H₂-TPR、CH₄-TPR、O₂-TPD和BET等分析技术对氧载体进行了表征。研究了不同Fe₂O₃负载量氧载体的甲烷化学链燃烧性能,考察了不同制备方法对Fe₂O₃/Al₂O₃氧载体结构、反应性和产物选择性的影响。结果表明,Fe₂O₃负载量对氧载体活性及产物中CO₂选择性的影响较大,负载量较低时氧载体活性较低且引起甲烷部分氧化产物CO含量增加。制备方法亦对氧载体与甲烷的反应活性有所影响,整体上共沉淀法制备的质量分数60％Fe₂O₃/Al₂O₃氧载体具有较高的氧化活性和化学链循环稳定性。其在反应温度850℃、反应时间15 min、30次循环后甲烷转化率及产物中CO₂选择性均未见明显降低。     

V_2O_5/Ti-Ce-PILC在H_2S选择性催化氧化过程中的催化性能

合成了TiO_2-CeO_2柱撑黏土负载V_2O_5催化剂,通过XRD、氮气吸附脱附、TG、FT-IR、H_2-TPR、NH_3-TPD、XPS等方法对其物理化学性质进行了表征,研究了该催化剂在H2S选择性催化氧化反应中的活性。结果表明,负载5%V_2O_5的TiO_2-CeO_2柱撑黏土在180℃下催化效果最好,且尾气中不含SO_2。V_2O_5、TiO_2和CeO_2之间的相互作用提高了催化剂的活性,CeO_2提高了催化剂的热稳定性,同时提供大量晶格氧,加强了V_2O_5的氧化还原作用,降低了反应温度;TiO_2加强了VO_x和CeO_x的再氧化,降低了硫酸盐的覆盖率,从而降低了催化剂的失活速率。     

pH and H2O2 dual-responsive carbon dots for biocatalytic transformation monitoring

Carbon dots with strong orange light emission, pH and H₂O₂ dual-responsive characteristics, were prepared and applied for probing enzyme-mediated biocatalytic transformations via the fluorescence quenching.     

γ-Al2O3对SCR脱硝催化剂V2O5-WO3/TiO2的改性研究

采用溶胶凝胶法制备了不同γ-Al₂O₃含量的钛铝复合载体,以此为载体采用浸渍法负载V₂O₅和WO₃制备了一系列催化剂。采用X射线衍射(XRD)、比表面积测定(BET)、程序升温还原(H₂-TPR)、高分辨率透射电子显微镜(HRTEM)等表征技术对催化剂表面形态进行分析,同时在模拟氨气选择性催化还原NO(NH₃-SCR)的反应条件下,对催化剂的脱硝反应活性和SO₂抗中毒进行考察。结果发现,TiO₂和γ-Al₂O₃之间的协同作用使得V₂O₅-WO₃/TiO₂-γ-Al₂O₃催化剂的脱硝效率及活性窗口明显优于单一载体制备的催化剂,表现出了良好的热稳定性和抗SO₂毒化能力,特别是V₂O₅-WO₃/TiO₂-15% γ-Al₂O₃在310~460 ℃,NO的转化率均在80%以上,反应窗口最宽。各种表征结果表明,TiO₂-γ-Al₂O₃复合载体中γ-Al₂O₃高度分散在TiO₂上,复合载体具有较大的比表面积,同时具有较强的还原能力。     

Dy和Y掺杂改性对CuO/CeZrO_2催化剂在富氢气氛中CO优先氧化催化性能的影响

采用水热-浸渍法制备了系列Dy和Y掺杂改性的CuO/CeZrO_2催化剂,使用X射线粉末衍射(XRD)、N_2吸附脱附和程序升温还原(H_2-TPR)等手段对催化剂进行了表征,研究了Dy和Y掺杂改性对CuO/CeZrO_2在富氢气氛中CO优先氧化催化性能的影响。结果表明,所制备的CuO-CeZrO_2催化剂均为萤石结构;添加适当比例的Dy_2O_3和Y_2O_3能增强活性组分与载体间的相互作用,有利于CuO活性组分的分散和低温还原能力的提高,从而改善了CuO/CeZrO_2用于CO优先氧化的催化活性。同时,掺杂Dy和Y能够提高CuO/CeZrO_2催化剂的抗CO_2抑制作用的能力,改善其催化稳定性。     

H2O2-based epoxidation of bridged cyclic alkenes with [P{Ti(O2)}2W10O38] in monophasic systems: active site and kinetics

The H₂O₂-based epoxidation of bridged cyclic alkenes in a monophasic system containing low concentrations (<2 mM) of [Bu₄ⁿN]₄[Pr₂ⁱNH₃]₂H[P{Ti(O₂)}₂W₁₀O₃₈]·H₂O (1) (with two η²-peroxotitanium sites in the anion) has been studied in search of the catalytically active species involved. ³¹P NMR spectra of 1, measured under a variety of conditions, revealed that the active species was not hydroperoxotitanium complex [P{Ti(OOH)}₂W₁₀O₃₈]⁷⁻or [P{Ti(OOH)}Ti(O₂)W₁₀O₃₈]⁷⁻. The reaction pathways for the alkene epoxidation are discussed to understand the kinetics (especially the initial [H₂O₂] dependence). It was concluded that the net catalytic reaction for the epoxidation occurred through the two-electron oxidation at the hydroperoxotitanium site in the catalyst.     

The decomposition of H2O2 catalyzed by polymer supported transition metal complexes

The synthesis and use of nitrogen-containing copolymers for anchoring Ru(II) and Rh(I) species is described. The supported species are effective as catalysts for the decomposition of H₂O₂ in aqueous medium at neutral pH. The polymers as well as the supported catalysts have been characterised by physical and chemical methods. The effects of [H₂O₂], catalyst loading and pH of the medium on the rate of decomposition have been studied. Suitable mechanisms have been proposed to account for the kinetics. Recycling efficiencies of the catalysts are found to be good.     

Co/Fe/Al2O3/cordierite催化C3H6选择性还原NO的实验研究

采用溶胶凝胶法和浸渍法制备了负载于蜂窝陶瓷上的Co/Fe/Al₂O₃/cordierite催化剂,在陶瓷管流动反应器上对其催化C₃H₆选择性还原NO的性能进行了测试。结果表明,该催化剂表现出最优脱硝性能,在模拟烟气条件下,当反应温度为550 ℃时可实现97%的脱硝效率。Co的引入可显著增强Fe/Al₂O₃/cordierite催化剂抗SO₂和H₂O的能力。在模拟烟气中同时引入0.02% SO₂和3% H₂O后,1.5Co/Fe/Al₂O₃/cordierite的脱硝性能受影响甚微,当反应温度高于500 ℃时1.5Co/Fe/Al₂O₃/cordierite催化C₃H₆还原NO的效率均可达到90%以上;相比之下,未经Co修饰的催化剂Fe/Al₂O₃/cordierite脱硝性能受到了严重的抑制,在整个反应温度区间（200-700 ℃）内,其催化C₃H₆还原NO的效率最高不足50%。XRD和SEM表征结果表明,经过适量的Co修饰后的1.5Co/Fe/Al₂O₃/cordierite表面变得更疏松,且形成了以钴铁和钴铝双金属氧化物为主要成分的球状晶粒。H₂-TPR结果表明,相比于Fe/Al₂O₃/cordierite,1.5Co/Fe/Al₂O₃/cordierite有更好的低温还原性能。Py-FTIR结果表明,Co的引入可使催化剂表面的Lewis酸明显增加,且生成了Brønsted酸。N₂吸附-脱附表征结果表明,Co可增大催化剂的比表面积。     

富含光诱导氧空位Bi12O17Br2的制备及其高效光催化固氮性能(英文)

采用一步水热法制备了Bi₁₂O₁₇Br₂光催化剂,其平均微片尺寸为1.2μm,比表面积约为29 m²·g^-1。Bi₁₂O₁₇Br₂的禁带宽度为2.42 eV,能够响应可见光。值得注意的是,在光照条件下Bi₁₂O₁₇Br₂表面能够产生氧空位;光诱导氧空位不仅能促进氮气在催化剂表面的吸附,而且对吸附的氮气分子的活化起到至关重要的作用。实验结果表明在可见光照射下,Bi₁₂O₁₇Br₂光催化剂上的氨生成速率为337.6μmol·g^-1·h^-1。在可见光的驱动下,Bi₁₂O₁₇Br₂光催化剂能够实现氮气与水反应生成氨的过程。     

基于金属卟啉2DMOFs仿酶催化的过氧化氢比色法检测

以四（4-羧苯基）铁卟啉（FeTCPP）作为有机配体,铜离子作为金属节点,利用溶剂热法制备了双金属Cu-FeTCPP金属有机骨架（MOFs）材料,并采用表面活性剂辅助法合成了二维纳米片（Cu-FeTCPP 2DMOFs）.该纳米片呈超薄的纳米结构,与三维块体结构（3DMOFs）相比具有更大的比表面积.基于Cu-FeTCPP 2DMOFs的仿酶特性,将其用于催化过氧化氢（H₂O₂）氧化底物3,3',5,5'-四甲基联苯胺（TMB）显色,根据显色产物吸光度与H₂O₂浓度之间的正比关系实现了对H₂O₂的测定.经稳态动力学分析发现,底物相同时该纳米片的米氏常数K_m均比Cu-FeTCPP 3DMOFs的K_m小,表明纳米片与底物之间有更好的亲和力,这归因于二维结构大的比表面积和较多易接近的活性位点.基于Cu-FeTCPP 2DMOFs构建的比色检测方法在优化条件下对H₂O₂的线性检测范围为3~1000 μmol/L,检出限为2.08 μmol/L,在水体中H₂O₂的检测方面具有良好的应用前景.     

Hydrothermal Synthesis of H3PW12O40/TiO2 Nanometer Photocatalyst and Its Catalytic Performance for Methyl Orange

H3PW12O40/TiO2 nanometer photocatalyst was prepared by one step hydrothermal synthesis from H3PW12O40′nH2O and Ti(OBu)4,simultaneously realizing the load and modification of H3PW12O40.The catalyst was ...     

耐硫甲烷化中H2S浓度对MoO3/Al2O3和CoO-MoO3/Al2O3催化剂的影响

在0 到12 mL·L^-1 (体积分数φ=0.00%-1.20%) 范围内考察了不同H₂S 浓度对25% (质量分数, w)MoO₃/Al₂O₃和5% (w) CoO-25%MoO₃/Al₂O₃催化剂甲烷化性能的影响. 结果表明, 5%CoO-25%MoO₃/Al₂O₃的甲烷化活性随H₂S浓度的增加单调上升, 而25%MoO₃/Al₂O₃对H₂S浓度并不敏感. 对比这两种催化剂发现, 只有在H₂S浓度高于0.40% (φ) 时, 在25%MoO₃/Al₂O₃中添加Co助剂才会有促进作用; H₂S浓度低于0.40% (φ)时, Co助剂会抑制25%MoO₃/Al₂O₃催化剂的甲烷化活性. 分别对反应前后的催化剂表征发现, H₂S浓度的改变不会对两种催化剂的物理结构产生明显的影响, 而是通过影响催化剂表面的金属硫化物活性位来影响催化剂的甲烷化性能. 耐硫甲烷化反应体系中较高的硫含量下Co助剂才表现出对25%MoO₃/Al₂O₃催化剂的促进作用. 该研究明确了在MoO₃/Al₂O₃催化剂中添加Co助剂的硫化氢浓度范围, 为工业上选择合适的催化剂提供了依据.     

铝源对Ni/Al2 O3催化剂结构及其CO2-CH4重整性能的影响

以三种不同铝源采用溶液燃烧法制备了系列Ni/Al_2O_3催化剂,通过XRD、H_2-TPR、NH_3-TPD、N_2吸附-脱附、TGDTG和TPH等分析方法对反应前后催化剂进行了表征,研究了铝源对Ni/Al_2O_3催化剂结构、表面性质及其CO_2-CH_4重整性能的影响。结果表明,以Al(NO_3)_3·9H_2O为铝源制备的NiNO-AlNO催化剂比表面积较大,达102 m~2/g;高温还原峰面积大,峰型更为弥散;且载体Al_2_O_3具有一定的结晶性。而以Al_2(SO_4)_3·18H_2O和AlCl_3·6H_2O为铝源制备的NiNO-AlSO和NiNO-AlCl催化剂,其载体以无定型Al_2O_3存在,活性组分Ni晶粒粒径大、分散性差,还原峰面积较小,与载体的相互作用较弱。其中,由于硫酸铝较为稳定,需要在更高温度下才能转化为Al_2O_3,且所制备NiNO-AlSO催化剂中残留有含硫物质,使得其表面酸性较强。评价结果显示,NiNO-AlNO催化剂活性较高,稳定性好,CH4转化率为31.21%,CO_2转化率为48.97%。积炭分析结果发现,NiNO-AlNO催化剂表面积炭量最少,沉积炭主要以无定型态存在,具有良好的抗积炭性能。