Enhancement of photoinduced hydrogen production from irradiated Pt/TiO2 suspensions with simultaneous degradation of azo-dyes

The production of hydrogen from aqueous Pt/TiO₂ suspensions illuminated with UV–vis light has been examined in the absence and in presence of azo-dyes in solution. The effects of operational variables, including dye concentration, solution pH and temperature, on the rate of hydrogen production were investigated. It has been found that deposition of Pt (0.5 wt.%) on the semiconductor surface results in an increase of the H₂ production rate, which goes through a maximum with time of irradiation and then drops to steady-state values comparable to those obtained over bare TiO₂. Both, maximum and steady-state rates obtained over Pt/TiO₂ suspensions were found to increase with increasing solution pH and temperature. Addition of small quantities of azo-dyes in solution results in significantly enhanced rates of H₂ production for a period which depends on dye concentration, solution pH and, to a lesser extent, solution temperature. It is proposed that the dye acts as a scavenger of photogenerated oxidizing species while it is degraded toward CO₂ and inorganic ions. When complete mineralization is achieved, oxygen can no longer be removed from the photocatalyst surface and the rate drops to steady-state values, comparable to those obtained in the absence of azo-dye in solution. The amount of additional H₂ produced is directly proportional to the amount of dye added in the solution. The rate increases with increasing solution pH, where dye degradation is faster, indicating that the process is limited by the rate of consumption of photogenerated oxygen. It is concluded that, under certain experimental conditions, it is possible to obtain significantly enhanced rates of photoinduced hydrogen production from Pt/TiO₂ suspensions with simultaneous mineralization of azo-dyes. The process could be used for combined production of fuel H₂ and degradation of organic pollutants present in water.     

Reduction of carbon dioxide with water under concentrated sunlight using photocatalyst combined with Fe-based catalyst

The reduction of CO₂ with water into valuable organic compounds under concentrated sunlight was investigated for the first time over a hybrid catalyst, in which a Pt-loaded K₂Ti₆O₁₃ photocatalyst was combined with a Fe-based catalyst supported on a dealuminated Y-type zeolite (Fe-Cu-K/DAY). In this reaction system, the Pt/K₂Ti₆O₁₃ catalyst decomposes water to produce H₂ and the Fe-Cu-K/DAY catalyst reduces CO₂ with the resulting H₂ into organic compounds. When only the Pt/K₂Ti₆O₁₃ photocatalyst was used, organic compounds such as CH₄, HCOOH, and HCHO were formed together with H₂, indicating that CO₂ can also be directly reduced over Pt/K₂Ti₆O₁₃. On the contrary, when the hybrid catalyst was used, CH₃OH and C₂H₅OH were produced in addition to the above products, depending on the reaction temperature and catalyst composition. The reaction temperature significantly increased by concentrating the solar irradiation, reaching 600 K and increasing the product yields. It is suggested that such a high reaction temperature facilitates both the photoreduction and hydrogenation of CO₂ over Pt/K₂Ti₆O₁₃ and Fe-Cu-K/DAY, respectively.     

Effect of gas composition on nitric oxide removal from simulated flue gas with DBD-NPC method

A new method for nitric oxide (NO) removal was developed by combining dielectric barrier discharge (DBD) and negative pulse corona (NPC). The effects of gas composition (O₂, CO₂, and H₂O) on NO removal were investigated with this method, and the effect of alcohols (methanol and ethanol) addition on NO removal was also investigated as well as the reaction mechanisms to enhance the NO removal efficiency. The experimental results showed that O₂, CO₂, and H₂O had obvious inhibition effects on NO removal, and the negative effects were in the following order:O₂ > CO₂ > H₂O. The addition of methanol or ethanol in the reaction system could mitigate the negative effects of O₂, CO₂, and H₂O on NO removal, and also eliminated the production of NO₂. The positive effect of alcohols addition with DBD-NPC denitration method was also validated in the simulated flue gas, in which the NO_x (NO, NO₂) was mainly converted into N².     

Synthesis of mixed alcohols from CO2 contained syngas on supported molybdenum sulfide catalysts

The performances of active carbon supported molybdenum sulfide catalysts prepared by different procedures or promoted by different elements in the synthesis of mixed alcohols from CO₂ containing syngas were examined. The results showed that high alcohol activity and selectivity could be obtained by employing a rapid drying procedure and employing a H₂S---H₂ stream for (NH₄)₂MoS₄ decomposition. Addition of Co, Cr and Cl to K---Mo/C catalyst led to an increase in the alcohol activity or selectivity. The presence of CO₂ in the feed caused a greater amount of water to be produced but reduced the formation of CO₂. The product distribution was also strongly influenced by the presence of either CO₂ or H₂S in the feed. Addition of CO₂ reduces the formation of higher alcohols while H₂S increases higher alcohol formation.     

Blautia coccoidesGA-1的传代培养及其同化H2/CO2产乙酸特征

为了解同型产乙酸菌异养代谢与自养代谢的相互作用与机制,并为快速获得具有较强自养代谢能力的菌体细胞提供培养方法,以H₂/CO₂和(或)葡萄糖为碳源,考察了Blautia coccoidesGA-1在连续传代培养中的代谢特征。结果表明,以H₂/CO₂作为唯一碳源进行连续传代培养时,菌株GA-1长势较弱,其子代的自养代谢能力也逐渐下降;在葡萄糖培养基中,菌株GA-1增殖旺盛,但高浓度的葡萄糖对其自养代谢能力有显著抑制作用,这种抑制作用可能是自养代谢和异养代谢对辅酶A和ATP的竞争、酸性环境造成的代谢抑制以及辅酶I的氧化还原平衡调节等综合作用的结果。以体积比为4:1的H₂/CO₂混合气为气相条件,用200mg·L^-1葡萄糖培养基对菌株GA-1进行传代培养,不仅可获得稳定的子代培养物,而且可以将其利用H₂/CO₂产乙酸的能力维持在2.16g乙酸·(g干细胞)^-1的水平。     

铜基催化剂还原过程研究综述

铜基催化剂广泛应用于工业生产中,催化剂还原是催化剂生产的最后一道工序,也是工业使用前的第一个步骤,对几种铜基催化剂的还原过程进行综述。铜基催化剂主要应用于CO与H_2合成甲醇和CO低温变换,也可用于CO_2与H_2合成甲醇以及脂肪酯加氢制脂肪醇。铜基催化剂的还原方法主要有液相还原法和气相还原法,其中,气相还原法用途较广。对影响还原的条件(H_2浓度、温度、压力和空速等)及杂质(H_2O、O_2和CO_2等)进行总结,并以甲醇合成催化剂为例对低氢还原法和高氢还原法作了介绍。     

Photocatalytic syngas synthesis from CO2 and H2O using ultrafine CeO2-decorated layered double hydroxide nanosheets under visible-light up to 600 nm

The rational design of photocatalyst that can effectively reduce CO₂ under visible light(l>400 nm),and simultaneously precise control of the products syngas(CO/H2)ratio is highly desirable for the Fischer-Tropsch reaction.In this work,we synthesized a series of CeO₂-decorated layered double hydroxides(LDHs,Ce-x)samples for photocatalytic CO₂ reduction.It was found that the selectivity and productivity of CO and H₂ from photoreduction of CO₂ in conjunction with Ru-complex as photosensitizer performed an obvious“volcano-like”trend,with the highest point at Ce-0.15 and the CO/H₂ ratio can be widely tunable from 1/7.7 to 1/1.3.Furthermore,compared with LDH,Ce-0.15 also drove photocatalytic CO₂ to syngas under 600 nm irradiation.It implied that an optimum amount of CeO₂ modifying LDH promoted the photoreduction of CO₂ to syngas.This report gives the way to fully utilize the rare earth elements and provides a promising route to enhance the photo-response ability and charge injection efficiency of LDH-based photocatalysts in the synthesis of syngas with a tunable ratio under visible light irradiation.     

g-C3N4-CdS-NiS2复合纳米管的制备及可见光催化分解水制氢

光生电子-空穴对的快速复合是导致半导体光催化剂性能不佳的重要因素之一,构建异质结是分离光生电子-空穴对的有效方法。结合热缩合和两步水热反应构建了g-C₃N₄-CdS-NiS₂复合纳米管,并进一步研究了在可见光照射下不同CdS含量的g-C₃N₄-CdS-NiS₂分解水制氢的光催化性能。结果表明,当CdS含量为10%(质量)时,三元复合物的产氢速率最高(50.9 μmol·h^-1),是纯g-C₃N₄纳米管的25倍,是g-C₃N₄-CdS和g-C₃N₄-NiS₂二元复合物的11倍。而且,经过五次循环光催化反应后,产氢速率保持不变。光催化制氢性能的提高主要源于g-C₃N₄、CdS与NiS₂形成的异质结促进光生电子和空穴的迁移及电子-空穴对的分离。     

Photocatalytic degradation of model organic pollutants on an immobilized particulate TiO2 layer: Roles of adsorption processes and mechanistic complexity

The kinetics of photocatalytic degradation of four different model organic compounds, formic acid (FA), oxalic acid (OA), 4-chlorophenol (4-CP) and the herbicide monuron (3-(4-chlorophenyl)-1,1-dimethylurea) in a self-constructed batch-mode plate photoreactor with a thin flow of contaminated aqueous solution circulating over an illuminated particulate layer of TiO₂ P25 (Degussa) was compared. Both OA and FA were adsorbed on TiO₂ surface; their mineralization, induced by direct transfer of photogenerated holes, proceeded in a single step, without observable intermediates, following approximately zero order kinetics. Numerical simulations were performed using a newly proposed kinetic model based on the photostationary state assumption. The model allowed an explanation of the observed reaction order as well as the comparison of independent with competitive adsorption of organic compound and oxygen on the photocatalyst surface, yielding a better fit for the case of competition. 4-CP and monuron, which were not adsorbed under the conditions used, were degraded through the action of photogenerated hydroxyl radicals. Their degradation proceeded with lower photoefficiency than for the adsorbed compounds (FA and OA). While the mineralization of both 4-CP and monuron followed zero order kinetics, their degradation was close to first order. The different reaction orders were consistently explained using the photostationary state approach.     

温度对厌氧耗氢产甲烷的影响研究进展

化石燃料燃烧过程中大量排放的CO₂引起了人们对CO₂生物甲烷化的关注。厌氧有机物生物降解过程中，与CO₂生物甲烷化相关的主要是厌氧耗氢产甲烷菌。近年来，研究者们关注温度对厌氧耗氢产甲烷过程的影响，对推动厌氧耗氢产甲烷工艺的发展有着重要的意义。本文从厌氧耗氢产甲烷技术原理出发，介绍了厌氧生物降解过程中耗氢产甲烷菌的重要作用，归纳了32种仅利用H₂和CO₂产CH₄的专性耗氢产甲烷菌，展示了氢气可以来源于化石燃料、生物质、水的分解和工业气体，综述了不同温度范围下厌氧耗氢产甲烷的效能，总结了不同温度变化方式对厌氧耗氢产甲烷的影响，并从氢气来源和温度变化等方面提出了展望。     

Aspen Plus模拟高浓度H2S/CO2酸性气的选择性分离

以煤制氢尾气中的高浓度酸性气体H₂S和CO₂为对象,以聚乙二醇二甲醚（NHD）为吸收剂,使用PC-SAFT状态方程拟合了酸性气体CO₂和H₂S在聚乙二醇二甲醚（NHD）溶剂中溶解参数,运用Aspen Plus流程模拟软件,构建两级吸收分离工艺,实现H₂S和CO₂的高效分离,H₂S浓度由30%提升至98.7%,CO₂含量由55%提升至99.4%。由此,可以通过高效分离酸性气H₂S和CO₂,并以提浓后再资源化利用的方式实现酸性气的污染控制。     

吸附强化焦油蒸汽重整制取氢气

分别采用固相反应法、溶胶凝胶法制备了Ni/Mg-Ca₁₂Al₁₄O₃₃催化剂、CaO-Ca₁₂Al₁₄O₃₃吸附剂,并将其作为重整催化剂、CO₂吸附剂应用在焦油蒸汽重整制取氢气的研究中,通过与普通蒸汽重整进行对比,系统地研究了重整温度、S/C比（反应体系中水蒸气与碳元素的摩尔比）、质量空速对焦油吸附强化蒸汽重整制氢特性的影响。结果表明,CO₂吸附剂的加入能够有效提升焦油重整效果,氢气产率、体积分数均得到显著提高,其中氢气体积分数达95%以上。随着S/C比的增加、质量空速的减小,普通蒸汽重整和吸附强化重整的制氢效果均是增强的,且均在S/C比、质量空速分别达到12：1、0.128 h⁻¹后增幅不再明显;尽管如此,相比普通重整,吸附强化重整降低了最佳重整制氢温度,在800℃时氢气产率能够达到87.35%。     

ALTERNATIVE GENERATION OF H2, CO AND H2, CO2 MIXTURES FROM STEAM-CARBON DIOXIDE REFORMING OF METHANE AND THE WATER GAS SHIFT WITH PERMEABLE (MEMBRANE) REACTORS

A new process is proposed which converts CO₂ and CH₄ containing gas streams to synthesis gas, a mixture of CO and H₂ via the catalytic reaction scheme of steam-carbon dioxide reforming of methane or the respective one of only carbon dioxide reforming of methane, in permeable (membrane) reactors. The membrane reformer (permreactor) can be made by reactive or inert materials such as metal alloys, microporous ceramics, glasses and composites which all are hydrogen permselective. The rejected CO reacts with steam and converted catalytically to CO₂ and H₂ via the water gas shift in a consecutive permreactor made by similar to the reformer materials and alternatively by high glass transition temperature polymers. Both permreactors can recover H₂ in permeate by using metal membranes, and H₂ rich mixtures by using ceramic, glass and composite type permselective membranes. H₂ and CO₂ can be recovered simultaneously in water gas shift step after steam condensation by using organic polymer membranes. Product yields are increased through permreactor equilibrium shift and reaction separation process integration.

CO and H₂ can be combined in first step to be used for chemical synthesis or as fuel in power generation cycles. Mixtures of CO₂ and H₂ in second step can be used for synthesis as well (e.g., alternative methanol synthesis) and as direct feed in molten carbonate fuel cells. Pure H₂ from the above processes can be used also for synthesis or as fuel in power systems and fuel cells. The overall process can be considered environmentally benign because it offers an in-situ abatement of the greenhouse CO₂ and CH₄ gases and related hydrocarbon-CO₂ feedstocks (e.g., coal, landfill, natural, flue gases), through chemical reactions, to the upgraded calorific value synthesis gas and H₂, H₂ mixture products.     

Conversion of sulfur dioxide to sulfate and hydrogen sulfide by Desulfotomaculum orientis

The autotrophic, sulfate-reducing bacterium, Desulfotomaculum orientis, grew in batch culture with molecular hydrogen (H₂) as an energy source, carbon dioxide (CO₂) as a carbon source and sulfur dioxide (SO₂) as the terminal electron acceptor. At high H₂ partial pressure, SO₂ was stoichiometrically reduced to hydrogen sulfide (H₂S). At low partial pressures of hydrogen (< 0.025 atm), SO₂ was both oxidized to sulfate and reduced to hydrogen sulfide. These results indicated a new mode of sulfur metabolism for D. orientis.     

利用外源氢气纯化升级沼气的研究进展

沼气发酵过程存在产气速率低和甲烷浓度低两个普遍问题。从甲烷生成的反应机理来看,如果提供充足的氢气,能够把沼气中的CO₂成分转化为CH₄,既提高了甲烷的产量,又提高了甲烷的浓度。介绍了最近国内外在这个方向上的探索性研究成果。实验表明,利用外源氢气确实可以纯化升级沼气,在一定条件下还可以达到生物甲烷的品质（即CH₄浓度高于95%）。分析了这项技术实用化需要解决的两个关键问题：强化H₂气液传质及获取廉价氢源。最后,对这个方向进行了展望,并提出了一个光电催化产氢与厌氧发酵产甲烷耦合的设想方案。     

Thermodynamic analysis of steam reforming of glycerol for hydrogen production at atmospheric pressure

Thermodynamic chemical equilibrium analysis of steam reforming of glycerol(SRG)for selective hydrogen production was performed based on the Gibbs free energy minimisation method.The ideal SRG reaction(C₃H₈O₃+3H₂O→3CO₂+7H₂)and a comprehensive set of side reactions during SRG are considered for the formation of a wide range of products.Specifically,this work focused on the analysis of formation of H₂,CO₂,CO and CH4 in the gas phase and determination of the carbon free region in SRG under the conditions at atmospheric pressure,600 K–1100 K and 1.013×10⁵–1.013×10⁶ Pa with the steam-to-glycerol feed ratios(SGFR)of 1:5–10.The reaction conditions which favoured SRG for H₂ production with minimum coke formation were identifies as:atmospheric pressure,temperatures of 900 K–1050 K and SGFR of 10:1.The influence of using the inert carrier gas(i.e.,N₂)in SRG was studied as well at atmospheric pressure.Although the presence of N₂ in the stream decreased the partial pressure of reactants,it was beneficial to improve the equilibrium yield of H₂.Under both conditions of SRG(with/without inert gas),the CH4 production is minimised,and carbon formation was thermodynamically unfavoured at steam rich conditions of SGFR>5:1.     

Highly effective conversion of carbon dioxide to valuable compounds on composite catalysts

The highly effective catalytic conversion of CO₂ into valuable compounds was investigated by multi-functional catalysts composed of base-metal oxides as the main components promoted by a low concentration of precious metals and gallium oxide. The desired reduced state of catalyst metal oxides for exhibiting the optimum catalytic performance could be controlled by both the hydrogen spillover on the precious metal parts and the inverse-spillover from the Ga parts. By applying those principal concepts in the catalyst structure-design, the rapid CO₂ reforming of methane, the rapid CO₂ methanation, the effective synthesis of methanol and/or ethanol from CO₂ and H₂, and selective syntheses of high quality gasoline and/or light olefins by means of one-pass conversion of CO₂-H₂ mixture via methanol as the intermediate product, were respectively realized. Those novel catalytic reactions would have a high potential to moderate the accumulation of CO₂ come from fossil fuel combustion, while compensating the cost of hydrogen as the reducing reagent.     

Modification of catalytic performances due to the co-feeding of hydrogen or carbon dioxide in the partial oxidation of methane over a NiO/γ-Al2O3 catalyst

The influence of the addition of 1–10 vol.% of hydrogen or carbon dioxide to the feed during the partial oxidation of methane was studied over a NiO/γ-Al₂O₃ catalyst. The addition of H₂ decreases the conversion and syngas selectivity. This decrease of performance seems to be related to a higher reduction of the catalyst due to the H₂ co-feeding. The addition of CO₂ also appears unfavorable to the production of hydrogen but increases the CO yield. A combination of the dry reforming and the reverse water gas shift reactions is suggested to explain the observed modifications in the product yields.     

钼酸铋半导体光催化剂的研究新进展

钼酸铋拥有典型的Aurivillius型结构,主要由(Bi_2O_2)~(2+)层及MoO_6钙钛片层状结构组成,显示出良好的光催化性能,广泛用于有机污染物的降解,成为近年来最受关注的一类可见光催化材料。综述钼酸铋半导体光催化剂的制备方法,以及通过构建异质结、掺杂、固溶体、金属沉积、量子点等改性措施提高其光催化活性,归纳和总结钼酸铋光催化剂在催化氧化反应、降解有机废水、电化学储能和CO_2的还原、气体传感器等方面的应用,并对钼酸铋光催化剂发展进行展望。     

基于CO2原位捕集的生物质热解制氢

以谷壳作为生物质研究对象,在石英管反应器中研究了基于CO₂原位捕集的谷壳热解制H₂,考察了不同温度、不同的CO₂捕集剂（CaO）配比对其热解的产气量、气体中H₂的体积分数的影响。实验结果表明,谷壳热解的产气量随温度的升高而增大,当反应温度在800℃时有最大产气量340mL/g;捕集剂CaO的添加通过原位吸收CO₂促进相关反应向生成氢气的方向移动。在600℃,不同比例CaO下CO₂体积分数都保持在22%左右,谷壳热解产生的气体中H₂的体积分数为14%~26%;在700℃,当CaO与生物质质量比为1：4时,添加CaO捕集剂能够较好地捕集CO₂,有效提高H₂的体积分数,此时获得较高的H₂产率41%,较低的CO₂体积分数16%,CaO的捕集率为64%;GC-MS表征分析发现,CaO在800℃的温度下对热解过程中产生的焦油有部分催化裂解效果。