CeO_2纳米棒负载Co催化CO脱除NO_x的机理

以碱法水热合成径向尺寸6~10nm的CeO_2纳米棒,采用湿法浸渍在纳米棒上负载不同含量的Co氧化物。通过实验探究Co含量改变对脱硝性能的影响原理,实验结果显示浸渍方案为3g CeO_2∶30ml 10%(质量分数)硝酸钴溶液时,脱硝效率最高,在NO与CO摩尔比为1∶5,体积空速为30000h~(-1),无氧状态下,250℃即能达到70%以上的效率。采用氮气吸附、XPS、TEM以及XRD测试不同钴含量催化剂的物化性质,与催化性能结果比对分析后得出Co的添加是通过改变催化剂表面的活性官能团来提高效率,其中Co_2O_3对于催化CO与NO_x进行反应具有较高的效率,提高催化剂中Co_2O_3的比重可以将高效率温度段降低,CoO在一定程度上对CO与NO_x反应具有负面作用,而Co_3O_4对低温阶段N_2O选择性影响较大。     

CeO2纳米纤维合成表征及催化降解甲基紫染料

水热法合成不同硅铈比Ce-MCM-41 介孔分子筛,用NaOH溶解脱除MCM-41介孔分子筛模板得到铈氧化物。采用 XRD、SEM、TEM、N2吸附-脱附等手段对其结构进行表征。结果显示,当n（Si/Ce）=1.0:1.0时,制备CeO2纳米纤维直径4nm,纤维长度500nm左右,比表面积528.0 m2.g-1,具有类似模板介孔分子筛MCM-41规则有序介孔形貌。将所制备CeO2纳米纤维用于催化过氧化氢氧化分解质量浓度为40mg/L甲基紫染料废水,经 45min 反应后甲基紫水溶液脱色率达80.0% 。     

逆уCeO2/CuχCo1-χOδ催化剂的制备 及其CO催化氧化性能

以Cu(NO_3)_2·3H_2O、Co(NO_3)_2·6H_2O、Ce(NO_3)_3·6H_2O和(NH_4)_2CO_3为原料,采用共沉淀法-浸渍法结合的制备方式,制得逆负载型уCe O_2/Cu_χCo_(1–χ)O_δ催化剂(у=0、5%、15%、25%;χ=0～1.0;δ=1.0～1.4)。通过XRD、BET、H_2-TPR、XPS考察了Cu O和Co_3O_4质量比[m(Cu O)∶m(Co_3O_4)]、表面Ce O_2负载量(у)(以Cu_χCo_(1–χ)O_δ质量为基准,下同)对逆负载уCe O_2/Cu_χCo_(1–χ)O_δ催化剂催化氧化CO性能的影响。结果表明,15%Ce O_2/Cu_(0.2)Co_(0.8)O_δ[m(Cu O)∶m(Co_3O_4)=0.2∶0.8]催化剂催化性能最佳。常压下,当反应温度为75℃时,CO转化率可达100%。由于15%Ce O_2/Cu_(0.2)Co_(0.8)O_δ比表面积较大,两相界面较多,进而使得Ce O_2与Cu—O—Co固溶体相互作用较强,表面存在较多的氧空穴、Cu~+和Co~(3+),催化剂还原温度较低,催化活性较好。     

纳米CeO2制备方法研究进展

对近年来国内外出现制备纳米CeO2的方法做了一下简单的介绍,重点分析了液相法中的沉淀法、溶胶-凝胶法、水热法、微乳液法的优缺点,指出了今后研究的重点和解决的主要问题。     

β-MnO2纳米棒催化H2O2降解刚果红的研究

采用热分解纳米结构γ-MnOOH前驱体制备出直径约200 nm、长度接近几十微米的β-MnO2纳米棒,通过XRD和TEM对产物进行了成分与形貌表征。β-MnO2纳米棒作为催化剂对H2O2分解刚果红具有良好的催化性能。实验研究了刚果红初始浓度、H2O2浓度和催化剂用量对刚果红脱色率的影响。进一步研究表明,β-MnO2纳米棒催化H2O2氧化降解刚果红的脱色反应属于2.44级动力学反应,反应速率常数为0.002834(mol/L)-1.44.min-1。经紫外-可见光谱、红外光谱分析表明,催化反应后刚果红分子结构遭到破坏。     

沉淀法制备纳米CeO2的研究

以硝酸铈、酒石酸铵为原料,采用沉淀法制备了CeO2纳米晶体,考察了煅烧温度、原料计量比和分散剂的影响,差热分析结果表明：前驱物为Ce2L3·8H2O,样品用TEM和XRD进行了表征,样品外观形貌为淡黄色蓬松状粉体,前驱物经600℃、700℃、800~C℃煅烧2h所得样品的粒径分别为15nm、24nm,32nm左右。     

Co/CeO2固体催化剂低温高效降解刚果红的研究

通过溶胶-凝胶法制备了掺杂含不同质量分数Co的Co/CeO2同体催化剂,对其催化降解有机染料刚果红的性能进行了研究.在常压.低温5～25℃范围内,采用催化湿式过氧化氢法（CWPO）对刚果红进行催化降解.结果表明,对于10 mg/L的刚果红模拟染料废水,当催化剂2.0wt％ Co/CeO2和氧化剂H2O2的投加量分别为0.07 g和0.02 mol/L时,反应30 min,反应温度20℃,刚果红的降解率高达99％,COD去除率可达82.8％,且催化剂的重复性实验表明催化剂具有良好的稳定性.     

水热法合成纳米CeO2及其光催化性质研究

用水热法制备了纳米CeO2,通过XRD、TEM、IR等测试手段对产物的物相结构、形貌和纳米尺度进行了表征.XRD分析表明,制得的纳米CeO2粒子为萤石结构且晶型比较完整;TEM表明产物颗粒基本为球形,且分散性较好,还分析了热处理温度对CeO2粒子大小的影响.以罗丹明B的光降解为模型反应,研究了在紫外光照射下的CeO2光催化活性,结果表明水热法制备的CeO2粒子,粒径小,吸光能力强,光催化活性高.     

CeO2在燃煤烟气汞脱除中的研究进展

综述了二氧化铈(CeO2)在燃煤烟气脱汞材料中的应用和在脱汞性能优化方面的研究进展,从CeO2的纯相、负载型、复合型材料三个方面对近年来CeO2提高材料的脱汞性能的相关研究进行总结,归纳了CeO2在不同脱汞材料中发挥的重要作用和脱汞过程中的反应,并展望了CeO2材料在烟气脱汞领域的未来发展前景.     

Carbon monoxide hydrogenation over cobalt catalyst in a tube-wall reactor: Part 1. Experimental studies

Effects of temperature (250?275°C), pressure (0.1-1.03 MPa) and feed gas exposure velocity (139-722 μm/s) were studied on carbon monoxide hydrogenation in a tube-wall reactor using plasma-sprayed cobalt catalyst. The specific catalytic activity and hydrocarbon selectivity increased with an increase in pressure and temperature and a decrease in the exposure velocity. The results showed that the formation of olefins especially ethylene and propylene was favored at low pressures, low temperatures and high exposure velocities. This catalyst was found to be selective for C₅⁺ hydrocarbons (27-34 wt.%) at increased pressures (0.69-1.03 MPa).     

Nitric oxide reduction by carbon monoxide over calcined limestone enhanced by simultaneous sulphur retention

Nitric oxide reduction by carbon monoxide over calcined limestones is enhanced by the coexistence of sulphur dioxide over a temperature range pertinent to f luidized-bed combustion. This demonstrates that the reduction of nitric oxide formed in fluidized-bed combustion of coal is promoted by simultaneous sulphur retention under a staged air firing. Thermogravimetric analysis indicated that the enhanced reduction of nitric oxide was attributed to the increase in catalytic activity of the calcined limestones used partially for sulphur retention.     

Carbon monoxide hydrogenation over cobalt catalyst in a tube-wall reactor: Part II. Modelling studies

A mathematical model was developed to predict the performance of Fischer-Tropsch Synthesis over cobalt catalyst in a tube-wall reactor. Comparison was made between model predictions and previous experimental results (part 1 of this paper) for pressures 0.35-1.03 MPa, temperatures 250?275°C, and exposure velocities 139-722 μ/s. The agreement was good. The model predicts an increase in methanation activity with temperature. Carbon monoxide and hydrogen conversions, and water and carbon dioxide concentrations increase along the reactor axis. With an increase in exposure velocity, hydrocarbons and carbon dioxide production increase, but water production decreases. However, the water-gas shift activity increases continuously along the reactor axis. The model is based on two-dimensional transport equations, and employs the orthogonal collocation method in its numerical predictions.     

Nitric oxide reduction and carbon monoxide oxidation over carbon-supported copper-chromium catalysts

Carbon supported copper-chromium catalysts are shown to be very active for both the reduction of nitric oxide with carbon monoxide and the oxidation of carbon monoxide with oxygen. Mixed copper-chromium oxide active phases have good activity in the simultaneous removal of nitric oxide and carbon monoxide from exhaust gases. The influence of several catalyst variables has been investigated. The activity per volume of catalyst increases with increasing loading, while the intrinsic activity shows a maximum around C/M=100−50. An optimum catalyst for nitric oxide reduction and carbon monoxide oxidation has a copper/chromium ratio of 2/1. The apparent activation energy for the carbon monoxide oxidation over carbon supported copper-chromium catalysts is 77 kJ/mol, suggesting that the Cu---O bond rupture is the rate-limiting process. The reduction of nitric oxide takes place at higher temperatures. Since all catalysts have a low selectivity for molecular nitrogen formation at lower temperatures, the dissociation of nitric oxide is probably rate determining, resulting in a slightly reduced catalyst system. In an excess of carbon monoxide the reaction is first-order in nitric oxide and zero-order in carbon monoxide. Moisture inhibits the reaction by reversible competitive adsorption, whereas carbon dioxide does not. Oxygen completely inhibits the reduction of nitric oxide due to the more rapid reoxidation of the catalytic sites compared to nitric oxide. Therefore, the reduction of nitric oxide takes place only when all oxygen has been converted and, hence, is shifted to higher temperatures. As a possible consequence, the production of nitrous oxide is reduced. Nitric oxide and molecular oxygen react preferentially with carbon monoxide, so, in an excess of oxidizing component, gasification of the carbon support occurs at higher temperatures after carbon monoxide has been completely consumed.     

Atom-economical reduction of carbon monoxide to methanol catalyzed by soluble transition metal complexes at low temperatures

Hydrocarbons and methanol are considered the preferred products of catalytic reduction of carbon monoxide derived from clean natural gas. In this paper, we focus on atom-economical synthesis of methanol catalyzed by soluble transition metal complexes as single-site catalyst precursors under mild reaction conditions. Of the metal systems reported in the literature, Ni complexes activated by alkoxide bases affected homogeneous CO reduction to methanol at low temperatures (80°–130°C) and low pressures (2000–5000kPa) to achieve CO conversion and methanol selectivity of >90 and >95, respectively. The involvement of mono- and multi- nuclear Ni species that readily interconvert under methanol producing conditions is invoked. A process based on such an active catalyst system would position methanol to be considered an inexpensive feedstock for the synthesis of other derivatives.To whom correspondence should be addressed. E-mail: devinder.mahajan@stonybrook.edu     

Silica-supported cobalt catalysts for the selective reduction of nitrogen monoxide with propene

Catalytic behavior of silica-supported transition metals for NO reduction with propene in the presence of oxygen was investigated. While both silica and cobalt oxides did not show any activity for the selective NO reduction, impregnated CoO/SiO₂ prepared from cobalt acetate showed good activity although the preparation conditions had significant effect on the activity. It was suggested that highly dispersed surface Co²⁺ ions on silica are responsible for the catalytic activity.     

纳米ZnO/CeO2复合氧化物的制备及其改性

以燃烧法制备氧化锌并以其为包裹对象用沉淀法合成ZnO/CeO₂复合氧化物,采用XRD、SEM 、IR、TG-DTA、UV-Vis、TEM对样品进行表征,结果表明氧化铈以包覆形式与氧化锌形成复合氧化物。用改性剂对复合氧化物进行改性研究,以亲油化度考察改性剂的类型、改性剂的用量、改性温度、pH值对改性效果的影响。实验结果表明:当选用硬脂酸钠为改性剂且用量为ZnO/CeO₂的4%,改性温度为60℃,pH值为7时,样品粒径明显变小,分散性变好,亲油化度明显提高,可获得最佳改性效果。     

Effects of modification of highly dispersed cobalt catalysts with alkali cations on the hydrogenation of carbon monoxide

In the hydrogenation of carbon monoxide, alkali cations were found to be effective as modifiers for highly dispersed cobalt catalyst to improve the selectivities of C₂-oxygenated compounds, especially acetic acid and acetaldehyde, and to increase the olefin/paraffin ratio of hydrocarbons. These effects are ascribed to depression of the hydrogenating ability of the catalyst by modification with alkali cations.     

电催化还原二氧化碳制一氧化碳催化剂研究进展

电催化还原CO₂作为缓解能源危机和全球变暖的有效途径已成为催化领域的研究热点。然而,不同反应途径的氧化还原电位较为接近,使产物的选择性成为电催化还原CO₂所需解决的主要问题。迄今为止,在水性电解质中可实现CO₂选择性地转化为一氧化碳（CO）和甲酸（HCOOH）。本文简述了电催化还原CO₂制CO的机理,包括CO₂吸附过程、二电子转移过程和CO脱附过程。从贵金属的晶面设计、形貌调控和表面功能化对反应活性和产物选择性的影响,铁卟啉、钴酞菁和镍三嗪在还原CO₂为CO反应中的电子转移途径,非金属碳基材料中杂原子和碳基质间的耦合效应等方面,重点介绍了近年来贵金属催化剂、过渡金属络合物催化剂和非金属碳基材料催化剂的研究进展,总结了各类催化剂的优缺点。指出在三类电催化还原CO₂制CO的催化剂中,非金属碳材料具有较高的CO法拉第效率,尤其是非金属碳材料成本较低、制备简单、结构易调控,在电催化还原中具有潜在的应用优势,是有望实现商业化应用的新型催化剂的候选材料之一。