Photocatalytic reduction of CO2 over Cu-TiO2 /molecular sieve 5A composite

TiO(2) and different Cu wt% loaded TiO(2) (TC(0.5-5.0)), 10 wt% TC(2.0) supported on molecular sieve 5A (10 wt% TC(2.0)/MS) were prepared by impregnation and solid-state dispersion methods. The photocatalysts prepared were characterized using XRD, SEM, and UV-Vis DRS, TEM, XPS spectroscopy techniques. Photocatalytic reduction of CO(2) in water and alkaline solution are investigated in a batch reactor. The yield of oxalic acid increased notably when TC was supported on molecular sieve. The Cu-TiO(2) supported on molecular sieve catalyst promotes the charge separation that leads to an increase in the selective formation of oxalic acid in addition to methanol, acetic acid and traces of methane. The product formation is due to the high adsorption of CO(2), water and product shape selectivity of the composite photocatalyst. The maximum yield of oxalic acid was found to be 65.6 μg h(-1) g(-1) per cat using 0.2 N NaOH containing solution over 10 wt% TC(2.0)/MS photocatalyst. The difference in the photocatalytic activity is related to its physicochemical properties.     

Promoting effect of chloride ions on selective oxidation of methanol to methyl formate over zirconia-supported ruthenium oxide catalysts

The effect of chloride ions on a monoclinic ZrO₂-supported RuO_x（RuO_x/m-ZrO₂） catalyst with a Ru surface density of 0.3 Ru/nm² was studied in the selective oxidation of methanol to methyl formate（MF） at a low temperature of 373 K.The m-ZrO₂ support was Cl-free,and Cl^- ions were introduced into the RuO_x/m-ZrO₂ catalyst by impregnation with zirconium oxychloride or ammonium chloride and subsequent thermal treatment in air at 673 K.The structures of these catalysts were characterized by X-ray diffraction,Raman and X-ray photoelectron spectroscopies.Their reducibility was probed by temperature-programmed reduction in H₂.The RuO_x domains were present as highly dispersed RuO₄^2- structure on m-ZrO₂ with similar reducibility for the RuO_x/m-ZrO₂ samples irrespective of modification with or without Cl^- ions.Introduction of appropriate amounts of zirconium oxychloride into RuO_x/m-ZrO₂ led to a remarkable increase in the methanol oxidation rate and MF selectivity,whereas introduction of ammonium chloride or zirconyl nitrate significantly inhibited the catalytic performance of RuO_x/m-ZrO₂.The promoting effect of Cl^- ions derived from zirconium oxychloride can be tentatively attributed to their roles in facilitating the adsorption of methanol and desorption of MF product or its intermediates.This finding provides novel insights into the promoting effect of Cl ions on oxides-based catalysts for selective oxidation reactions.     

液相还原法制备Cu/Zn/Al/Zr催化剂用于CO2加氢合成甲醇

近年来,由于大气CO2浓度增加引起的温室效应正日益威胁着人类的生存与发展,CO2的捕获与利用是有望解决温室效应和能源危机的有效途径.CO2催化转化为甲醇成为众多研究者关注的焦点,这是因为甲醇不仅是一种重要的基本化工原料,也是一种洁净的绿色燃料和能源载体.Cu基催化剂广泛应用于CO2加氢合成甲醇反应,并表现出良好的催化性能.通常,金属催化剂的制备是采用H2对金属氧化物进行还原.然而,传统的气相还原过程伴随着强烈的热效应,且需要在高温(473-573 K)下进行,会引起表面铜颗粒长大并加速其聚集烧结,使得活性组分利用率下降.近年来,以NaBH4为还原剂的液相还原法逐渐受到人们的重视,该方法操作简单、快捷且条件可控,反应在低温下进行,放出的热量可在液相环境中迅速得到转移,大大抑制了铜颗粒的聚集.因此,液相还原法可制备出高铜分散度、高活性的催化剂.焙烧温度对铜基催化剂结构和催化性能的影响已得到广泛探究,但这仅限于含二价铜物种催化剂,焙烧温度对含多种铜价态催化剂的影响未见报道.由于液相还原法制备的催化剂含有还原态的铜物种(Cu0和Cu+),它们比Cu2+具有更强的流动性,因此在后续的焙烧过程中催化剂更容易发生烧结和聚集.本文采用液相还原法合成了Cu/Zn/Al/Zr催化剂,分别于423,573,723和873 K焙烧后用于CO2加氢合成甲醇反应,考察了焙烧温度对制备的铜基催化剂结构性质和催化性能的影响,并与传统共沉淀法制备的催化剂进行了对比.结果显示,随着焙烧温度升高,铜物种聚集作用增强,金属铜颗粒尺寸增大,873 K时烧结出现显著增强.由于比表面积随焙烧温度升高而减小,高温度焙烧的催化剂具有小的表面碱性位数目.焙烧温度会影响催化剂中铜物种与其它组分的相互作用,进而影响催化剂的还原.随着焙烧温度的升高,催化剂的还原温度逐渐降低,表面Cu+/Cu0的比例先增后减.CO2加氢活性评价显示,液相还原法制备的催化剂具有更高的催化活性,尤其是甲醇选择性;随着焙烧温度升高,催化剂的CO2转化率和甲醇选择性先增后减,CZAZ-573催化剂具有最高活性,且在1000 h长周期活性测试中表现稳定.CO2转化率与催化剂暴露金属铜的比表面积密切相关.相比Cu0,产物甲醇更容易在Cu+表面催化生成,催化剂表面的Cu+/Cu0比与甲醇选择性的变化规律一致.通过调控焙烧温度可得到高Cu比表面积以及高Cu+/Cu0比的催化剂,有利于CO2加氢生成甲醇.     

SiO2负载Au-Pd双金属纳米颗粒催化甲醇选择性氧化合成甲酸甲酯

甲醇选择氧化制备甲酸甲酯（MF）是延伸甲醇产业链、开发高附加值下游产品的有效途径之一,负载型Au及Pd催化剂在这一反应中表现出优异的低温催化性能。为探索实用、高效和易再生的甲醇选择氧化催化剂,同时揭示双金属颗粒中Au和Pd的协同效应及甲醇氧化反应机理,本研究制备了一系列二氧化硅负载的Au-Pd催化剂（Au-Pd/SiO₂）,详细研究了其对甲醇选择氧化制甲酸甲酯的催化性能。结果表明,Au和Pd总负载量为0.6%、且Au/Pd质量比为2时,所制备的Au₂-Pd₁/SiO₂催化剂表现出优异的甲醇氧化催化性能;在130℃下,甲醇转化率达到57.0%,MF选择性为72.7%。多种表征结果显示,Au-Pd双金属纳米颗粒粒径为2-4 nm,高度分散于SiO₂载体表面,倾向于生成孪晶结构并暴露（111）晶面,这些因素是Au-Pd/SiO₂具有优异催化性能的主要原因。通过DRIFTS表征研究,提出了一个可能的MF生成机理：即甲醇首先与处于Au-Pd纳米粒子界面的表面氧作用,生成化学吸附的甲氧基;随后,甲氧基经去质子作用生成吸附的甲醛物种,后者与相邻的甲氧基物种亲核反应,并经β-H消除后得到目标产物MF。     

Structures and properties of zirconia-supported ruthenium oxide catalysts for the selective oxidation of methanol to methyl formate

The effects of RuO(x) structure on the selective oxidation of methanol to methyl formate (MF) at low temperatures were examined on ZrO(2)-supported RuO(x) catalysts with a range of Ru surface densities (0.2-3.8 Ru/nm(2)). Their structure was characterized using complementary methods (X-ray diffraction, Raman and X-ray photoelectron spectra, and reduction dynamics). The structure and reactivity of RuO(x) species change markedly with Ru surface density. RuO(x) existed preferentially as RuO(4)(2-) species below 0.4 Ru/nm(2), probably as isolated Zr(RuO(4))(2) interacting with ZrO(2) surfaces. At higher surface densities, highly dispersed RuO(2) domains coexisted with RuO(4)(2-) and ultimately formed small clusters and became the prevalent form of RuO(x) above 1.9 Ru/nm(2). CH(3)OH oxidation rates per Ru atom and per exposed Ru atom (turnover rates) decreased with increasing Ru surface density. This behavior reflects a decrease in intrinsic reactivity as RuO(x) evolved from RuO(4)(2-) to RuO(2), a conclusion confirmed by transient anaerobic reactions of CH(3)OH and by an excellent correlation between reaction rates and the number of RuO(4)(2-) species in RuO(x)/ZrO(2) catalysts. The high intrinsic reactivity of RuO(4)(2-) structures reflects their higher reducibility, which favors the reduction process required for the kinetically relevant C-H bond activation step in redox cycles using lattice oxygen atoms involved in CH(3)OH oxidation catalysis. These more reactive RuO(4)(2-) species and the more exposed ZrO(2) surfaces on samples with low Ru surface density led to high MF selectivities (e.g. approximately 96% at 0.2 Ru/nm(2)). These findings provide guidance for the design of more effective catalysts for the oxidation of alkanes, alkenes, and alcohols by the synthesis of denser Zr(RuO(4))(2) monolayers on ZrO(2) and other high surface area supports.     

Dehydrogenation of methanol to methyl formate over supported Ni, Pd and Pt catalysts. Anomalous catalytic functions of PdZn and PtZn alloys

Pd/ZnO and Pt/ZnO exhibited high catalytic performance for the dehydrogenation of methanol to methyl formate upon the formation of PdZn and PtZn alloys.     

Kinetic studies of methanol synthesis from CO_2+H_2 over copper based catalysts

The catalytic activity for the synthesis of methanol from carbon dioxide and hydrogen wasmeasured on various binary and ternary catalysts containing copper oxide under a pressure of 10 atm.Among these samples the catalysts, CuO/ZnO/γ-Al_2O_3, demonstrated the highest activity andselectivity to methanol; MnO, as third component, had no promotional effect on the activity of meth-anol formation. Based on a simple power rate law the apparent activation energy estimation and par-tial pressure dependence measurement were accomplished over eight catalysts. The activation energiesvaried from 40 to 120 kJ / mol depending on the composition of catalysts. The rates of methanol for-mation to be 0.3 -- 0.9 order in H_2 and about 0.1 -- 0.2 order in CO_2 were reported.     

Photocatalytic reduction of CO2 with H2O on TiO2 and Cu/TiO2 catalysts

Photoinduced reduction of CO₂ by H₂O to produce CH₄ and CH₃OH has been investigated on wellcharacterized standard TiO₂ catalysts and on a Cu²⁺ loaded TiO₂ catalyst. The efficiency of this photoreaction depends strongly on the kind of catalyst and the ratio of H₂O to CO₂. Anatase TiO₂, which has a large band gap and numerous surface OH groups, shows high efficiency for photocatalytic CH₄ formation. Photogenerated Ti³⁺ ions, H and CH₃ radicals are observed as reactive intermediates, by ESR at 77 K. Cu-loading of the small, powdered TiO₂ catalyst (Cu/TiO₂) brings about additional formation of CH₃OH. XPS studies suggest that Cu⁺ plays a significant role in CH₃OH formation.     

CuO-TiO2-ZrO2/HZSM-5催化CO2加氢制二甲醚

采用共沉淀法制备了一系列CuO含量不同（质量分数:50%-80%）的CuO-TiO₂-ZrO₂复合氧化物,并利用X射线衍射（XRD）、氮吸附（BET）、程序升温还原（H₂-TPR）、程序升温脱附（H₂/CO₂-TPD）和氧化亚氮（N₂O）反应吸附等多种方法对其进行了表征.以所制备的CuO-TiO₂-ZrO₂为甲醇合成活性组分与HZSM-5分子筛进行机械混合制成双功能催化剂CuO-TiO₂-ZrO₂/HZSM-5,在微型固定床流动反应器中,于250℃、3.0 MPa、H₂/CO₂（体积比2.8）以及空速1500 mL·g^-1·h^-1的条件下,对其催化CO₂加氢直接合成二甲醚（DME）的性能进行了评价.结果表明:随着CuO-TiO₂-ZrO₂中CuO含量的增加,CO₂的转化率先逐渐增大,至70%时达到最大,之后反而降低.DME的选择性随着催化剂中CuO含量的增加而增加,至≥70%时基本不变,故当CuO含量为70%时,DME的收率达到最大值（13.2%）.催化剂上合成含氧化合物（甲醇和DME）的活性与催化剂中金属铜的比表面积之间有较好的对应关系.     

In situ Raman spectroscopy studies for electrochemical CO2 reduction over Cu catalysts

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Theoretical insights into the mechanism of photocatalytic reduction of CO2 over semiconductor catalysts

Photocatalytic reduction of CO₂ is one important approach to alleviate greenhouse gas emission and energy crisis, which has gained huge attention in the past decades. However, the lack of understanding complex reaction mechanism impedes new catalysts design. It is also very difficult to understand the mechanism by using only experimental approaches. For this concern, theoretical calculations can effectively supplement the experimental deficiency and thus play an important role. Recently theoretical calculations have been performed on adsorption, migration and reduction of CO₂ molecule on the photocatalyst surface, leading to useful information that have contributed greatly to this field. This review summarizes recent advances in first-principles calculations about CO₂ photoreduction over various semiconductor photocatalysts like metal oxides, sulfides and g-C₃N₄. The methods, models, adsorption and reaction pathways have been discussed in detail. The perspective about future investigation on the photocatalytic reduction of CO₂ using first principles calculations is also presented.     

Conversion of methanol to hydrocarbons over metal-zeolite catalysts

Ni²⁺, Cr³⁺ and Pb²⁺ exchanged CaY zeolites including mixed forms like CrNiCaY and PbNiCaY were used to study methanol conversion. The selectivity of the reaction to olefin and paraffin formation depends on the type of samples, the activation of the catalyst and the reaction conditions.

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CaY , Ni²⁺, Cr³⁺ Pb²⁺- , CrNiCaY PbNiCaY, . - , .

     

MoO3-SnO2催化剂上二甲醚低温氧化高选择性制备甲酸甲酯

定向设计并制备了多功能MoO₃-SnO₂催化剂,在常压连续流动固定床反应器上实现了二甲醚低温氧化高选择性制备甲酸甲酯的过程。考察了机械混合法、共沉淀法及沉淀浸渍法等不同制备方法对催化剂性能的影响。在沉淀浸渍法制备的MoO₃-SnO₂催化剂上,常压、160℃反应条件下,甲酸甲酯选择性达94.1%,DME转化率也达到了33.9%,并且产物中无CO_x生成。采用NH₃-TPD、CO₂-TPD及H₂-TPR对催化剂进行了表征,结果表明,表面酸性、碱性及氧化性的不同是造成催化剂反应性能差异的原因。另外,通过采用XRD、Raman及TEM对催化剂结构进行表征发现,晶粒粒径及金属氧化物MoO₃的存在状态等结构的差异是造成催化剂活性不同的主要原因。较小晶粒的催化剂和表面存在的低聚态MoO₃是致使催化剂活性提高的主要原因。     

Selective electrocatalytic reduction of CO2 to formate by water-stable iridium dihydride pincer complexes

Iridium dihydride complexes supported by PCP-type pincer ligands rapidly insert CO(2) to yield κ(2)-formate monohydride products in THF. In acetonitrile/water mixtures, these complexes become efficient and selective catalysts for electrocatalytic reduction of CO(2) to formate. Electrochemical and NMR spectroscopic studies have provided mechanistic details and structures of key intermediates.     

Electrochemical CO2 reduction with earth-abundant metal catalysts

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The photocatalytic and thermal catalytic reduction of CO2 with H2 over Pt/TiO2 catalysts

浸渍法制备了Pt负载量为0.5 to 2%的Pt/TiO2催化剂,考察它们在光照和加热条件下二氧化碳催化加氢性能.结果表明,二氧化碳加氢反应均可在Pt/TiO2的催化下进行,但在不同反应条件下加氢反应通过不同方式进行.在加热条件下,二氧化碳可转化为一氧化碳和甲烷,且在低温加热条件下一氧化碳是主产物(CO选择性为100%,250℃,0.5%Pt/TiO2).在1.5%Pt/TiO2催化剂上,当反应温度从250℃升高到450℃时,CH4的选择性由0增加到60.94%.同时,增加Pt的负载量也会导致CH4的选择性的增加.然而,在光照条件下,产物只有甲烷.CO2-TPD结果表明,二氧化碳通过羰基基团与作为吸附中心的Pt相连接.结合催化活性与表征结果,提出在光照条件下,反应可能以二氧化碳和氢气分别被光生电子活化反应生成甲酸中间体,随后经由甲酸加氢和脱水生成甲烷的机理进行.而在加热条件下,反应可能以二氧化碳首先吸附在催化剂表面形成羰基Pt物种,随后加氢生成一氧化碳,一氧化碳继续加氢生成甲烷的机理进行.     

Nanostructured heterogeneous catalysts for electrochemical reduction of CO2

Electrochemical reduction of CO₂ provides a sustainable solution to address the intermittent renewable electricity storage while recycling CO₂ to produce fuels and chemicals. Highly efficient catalytic materials and reaction systems are required to drive this process economically. This Review highlights the new trends in advancing the electrochemical reduction of CO₂ by developing and designing nanostructured heterogeneous catalysts. The activity, selectivity and reaction mechanism are significantly affected by the nano effects in nanostructured heterogeneous catalysts. In the future, energy efficiency and current density in electrochemical reduction of CO₂ need to be further improved to meet the requirements for practical applications.