铜掺杂Zr0.4Ce0.6O2复合氧化物催化剂性能的研究

研究了铜掺杂Ｚｒ０．４Ｃｅ０．６Ｏ２复合氧化物的还原性和催化性能,结果表明,铜掺杂能显著提高昨合氧化物中氧化铈的还原性,降低氧化铜的还原温度,也能提高对ＣＯ氧化的催化活性和催化 这说明在铜与锆铈复合氧化物之间存在较强的相互作用,焙地催化剂样品的性能亦有一定影响。     

Ba、Co共掺MnOx复合氧化物低温选择性催化还原NO研究

利用柠檬酸络合法制备了一系列Ba、Co掺入MnO_x脱硝催化剂,研究了Ba、Co掺入对MnO_x低温NH₃-SCR性能的影响。测试结果表明：Ba单独掺入时抑制了MnO_x的催化性能,Co单独掺入时促进了MnO_x的催化性能;而当Ba、Co共掺时,催化剂性能出现了最大的提升,其中3BaMnCoO_x表现出了优异的脱硝活性,反应温度高于180℃时其脱硝性能在99%以上,且表现出了良好的抗水硫性能。采用XRD、SEM、NO-TPD、NH₃-TPD、H₂-TPR和NO吸附原位红外等表征手段对催化剂进行了表征。结果表明,Co掺杂后形成了MnCo₂O_4.5固溶体,赋予了催化剂优异的氧化还原性能;Ba掺杂为催化剂提供了新的NO吸附位点,导致了新的活性硝酸盐吸附物种形成,显著促进了催化剂的NO吸附性能。这些特性使得BaMnCoO_x低温脱硝催化剂展现出了优异的脱硝性能。     

铈锆复合氧化物制备方法进展

CexZr1-xO2具有良好的抗高温老化性能、低温还原性能及较高的储氧能力,可作为新一代三效催化剂的关键材料.本文较为全面的综述了铈锆复合氧化物各种制备方法进展.     

Mn-Fe-Ce/TiO_2低温NH_3选择性催化还原NO

采用浸渍法制备了MnO2-Fe2O3-CeO2/TiO2催化剂用于低温NH3选择性催化还原烟气中NO,考察了Mn, Fe, Ce含量及焙烧温度对NH3选择性催化还原NO的活性和抗水性能的影响. 在气体体积空速(GHSV)=24000 h-1, NH3/NO=0.8(j), 350℃煅烧和烟气含3%(j) O2的条件下,该系列催化剂的脱硝活性为MnO2-Fe2O3-CeO2/TiO2>MnO2- Fe2O3/TiO2>MnO2/TiO2,且在200℃时MnO2(10)-Fe2O3(5)-CeO2(5)/TiO2的脱硝率为95%. 对含10%(j)水蒸汽的烟气,MnO2(10)-Fe2O3(5)-CeO2(5)/TiO2的脱硝活性维持在87%;在10%(j)水蒸汽和100′10-6 SO2共存条件下,短时间内脱硝活性维持在55%.     

以锆铈固溶体为载体的金属氧化物催化剂对NO还原性能的研究

研究了负载于锆铈固溶体上的多种金属氧化物在富氧条件下,以丙烯为还原剂,选择性催化还原NO的性能,讨论了CeO<,2>含量,金属氧化物负载量对催化剂性能的影响.结果表明,CeO<,2>含量为25%,CuO负载量为5%时,催化剂的活性最好,350℃时NO转化率可达到64.8%.     

铈锆复合氧化物催化HCl氧化中相互作用机制

采用浸渍法制备了不同负载量的ZrO₂/CeO₂·（xZr/Ce）和CeO₂/ZrO₂·（yCe/Zr）两组催化剂。并采用XRD、Raman、N₂-Sorption、TEM和H₂-TPR等手段对xZr/Ce和yCe/Zr的结构和性质进行表征,并结合HCl催化氧化活性研究CeO₂与ZrO₂在反应体系中的相互作用。结果显示,CeO₂表面掺杂适量的Zr⁴⁺可以增加xZr/Ce表面氧空位浓度,提高其HCl氧化反应活性;但当CeO₂表面掺杂过量的Zr⁴⁺,Zr元素会以ZrO₂的形式存在于xZr/Ce表面,覆盖氧空位,降低了xZr/Ce的反应活性。对于yCe/Zr催化剂,ZrO₂表面高分散的CeO₂有利于催化活性的提高,但ZrO₂表层负载的CeO₂对催化活性的贡献具有阈值,当CeO₂负载量超过10%后,额外增加的铈物种对催化活性已无显著促进作用;对比发现xZr/Ce的氧空位主要来自于铈锆固溶体,yCe/Zr的氧空位主要来自于高分散的CeO₂,由铈锆固溶体产生的氧空位对活性提升更有利;与纯组分CeO₂相比,xZr/Ce与yCe/Zr两组催化剂在苛刻条件下的长期稳定性测试中均表现出高反应稳定性。     

Cr掺杂CeO2催化剂的结构性质及氮氧化物选择性催化还原机理的研究

使用密度泛函理论(DFT)计算对Cr掺杂CeO2催化剂的表面几何结构、电子性质以及其表面的氮氧化物选择性催化还原(NH3-SCR)反应机理进行了系统的研究.从头算热力学计算的结果表明,在实际反应条件下,Cr掺杂会导致催化剂表面被氧化从而形成富氧表面结构.态密度和Bader电荷的电子性质计算结果表明,Cr掺杂CeO2催化...     

Pt掺杂对Cu-Mn-Ce复合氧化物催化燃烧性能的影响

为提高复合氧化物催化剂的催化燃烧性能和热稳定性,采用溶胶-凝胶法制备一系列贵金属Pt改性的Cu-Mn-Ce催化剂,采用XRD、BET、H2-TPR、Raman对催化剂进行了表征,并以甲苯催化燃烧为模型反应考察了催化活性。结果表明,Pt掺杂会导致Cu-Mn-Ce晶相结构中出现较多的缺陷位,并使比表面积和表面氧数量增加,增强了催化剂的氧化-还原能力。活性测试表明,Pt相似文献   

新型铬钴复合氧化物中低温选择性催化NOx还原及原位机理研究

采用固相法合成系列铬钴复合氧化物催化剂,该催化体系在中低温[(180~300)℃]下具有优异的氨选择性催化氮氧化物还原活性,其中,Cr(0.5)-Cr Ox催化剂在空速50 000 h-1、反应温度200℃和220℃条件下,NOx转化率达100%。采用原位DRIFIS研究催化剂表面吸附物种以及催化机理,在反应温度220℃考察Cr(0.5)-Co Ox催化剂表面NH3与NO的吸附态形式和NH3-SCR反应过程中中间态及其反应机理。结果表明,Cr(0.5)-Cr Ox催化剂上NH3吸附在L酸位,也能吸附在B酸位,但只与气态的NOx反应,生成中间体NH2NO,再进一步反应,最终生成N2与H2O。吸附态的NOx不参与SCR反应,反应遵循Eley-Rideal机理。     

负载型锰铈复合氧化物SCR脱硝催化剂制备研究

采用复壁炭纳米管(CNTs)为载体,通过室温氧化还原法制备了锰铈复合氧化物低温NH_3-SCR脱硝催化剂Mn-CeO_x/CNTs。通过调节浸渍液的组成,考察了活性分锰铈配比对催化剂低温脱硝性能的影响。研究发现锰铈协同作用能够有效提高催化剂的低温脱硝性能,当Mn/(Ce+Mn)的摩尔比为0.6时,催化剂的低温活性最好,反应温度为160～180℃时脱硝率可达100%。该方法具有制备工艺简单、条件温和、低温脱硝效果好等优点。     

Selective Lean NO x Reduction over Metal Oxides

The present state of knowledge of NO _x reduction under lean conditions over metal oxides is summarized in this review, with an emphasis on the reaction mechanism. Although a number of nitrogen-containing intermediates have been observed and implied, including organic nitro, nitrite, cyanide, isocyanate, and ammonia, there is yet definitive observation that confirms the relevance of these to the principal reaction pathway. Individual component in a mixed oxide catalyst can participate at different stages of the NO _x reduction reaction. The nitrogen production efficiences for different oxide based catalysts are summarized, and their relationship to the nature of the catalyst is discussed.     

采用蜂窝状筛网催化剂进行NH_3选择性催化还原NO的反应

采用蜂窝状筛网催化剂用于以NH3为还原剂选择性催化还原 (SCR)NO的反应。考察了TiO2 负载量、催化剂组分、模件的齿高、催化剂长度以及筛网目数等因素对其催化行为的影响。结果表明 :8gTiO2 可将62 0cm2 的筛网模件表面完全覆盖 ,此时催化活性最佳。V( 1) W ( 3 ) /TiO2 的蜂窝状筛网催化剂表面存在聚合的钒基物种。催化剂长度大于 5cm时 ,不存在进口效应。筛网目数小于 2 4目时 ,NO转化率随筛网目数的增加而增加     

Kinetics of the Low-Temperature Selective Catalytic Reduction of NO with NH3 Over Activated Carbon Fiber Composite-Supported Iron Oxides

A kinetic analysis in a variety of conditions (gas composition and temperature) has been conducted on catalysts of iron oxides supported on activated carbon fiber composites (ACFC). Additionally, experiments of temperature-programmed desorption (TPD) of NO were conducted on the catalysts in order to reveal mechanistic features of the low-temperature SCR reaction. In the light of current SCR literature and previous work, a qualitative picture of the catalytic behavior of low-temperature SCR catalysts is offered. Apparently, the strength of adsorption of NO during the low-temperature SCR reaction is responsible for the governing reaction mechanism. Thus, highly stable nitrates formed on the surface provoke catalyst deactivation and reaction through an ER mechanism, with NO reacting from the gas phase, whereas the absence of these nitrates permits reaction of less stable nitrites from the catalyst surface, following an LH-type mechanism. This is the case for the ACFC-supported iron oxide catalyst analyzed in this work.     

Selective Catalytic Reduction of NO by NH3 on Sulfated Titanium-Pillared Clay

Structural, textural and surface properties of sulfated and non-sulfated titanium-pillared clay were correlated with catalytic tests in the reduction of NO by NH₃ in the presence of oxygen. Lower specific surface areas and basal spacings but stronger acid sites were observed on sulfated Ti-pillared clay than on Ti-pillared clay. Sulfated Ti-pillared clays were more active than Ti-pillared clay. Accordingly, it is suggested that the strong Brønsted acidity generated by sulfate is responsible for the high reactivity of sulfated Ti-pillared clay at high temperature.     

Effect of Sodium in Ferrierite on Selective Catalytic Reduction of NO by Acetylene

Influence of sodium in ferrierite (HFER) zeolite on selective catalytic reduction of NO by acetylene (C₂H₂-SCR) was investigated. NO _x -TPD and FT-IR indicated that small amount of sodium exchanged into the proton-form zeolite with an exchange level of about 11.8% is beneficial for the title reaction by accelerating active nitrate species formation on catalyst surface from NO₂ and by suppressing the reductant combustion. Nevertheless, no further improved catalytic performance in C₂H₂-SCR could be observed by a larger amount of sodium exchanged into HFER due to some inactive nitrate species formed on the zeolite. Instead, activity of the zeolite for C₂H₂-SCR was drastically reduced, since the capacity of the zeolite for catalyzing NO oxidation and accelerating active NO⁺ species formation was remarkably depressed.     

铁钨复合氧化物用于NH_3选择性催化还原NO

采用共沉淀法制备铁钨复合氧化物催化剂,用于NH3选择性催化还原NO,考察了Fe/W物质的量之比、反应空速、SO2和H2O对催化剂脱硝活性的影响,同时运用SEM、XRD、BET、NH3-TPD等表征手段对催化剂的微观形貌、晶型、比表面积、孔结构参数及表面酸性进行了分析。实验结果表明当n(Fe)∶n(W)=4∶1时,催化剂的反应活性最佳,其在300~400℃温度范围内及GHSV=75 000 h-1条件下NO转化率仍保持在90%以上,同时其也显示出较强的抗SO2和H2O中毒性能。通过表征发现Fe与W之间强烈的相互作用,较大的比表面积和催化剂较强的酸性是催化剂催化活性较好的主要原因。     

SCR of NO on Sulfated Zirconium Oxides in the Presence of Methane

Owing to the harmful influence of nitrogen oxides (NO_x) on the environment the legislative demands a reduction of NO_x emissions. This article is concerned with a screening of catalysts on the basis of sulfated zirconia for selective catalytic reduction (SCR) of NO_x with methane as reducing agent. To this end, sulfated zirconium oxides were doped with Ga, In, Fe, Ni, Ca and Ce as well as In + Ce oxides and catalytically tested. In addition, the influence of reaction parameters and catalytic poisons on SCR activity and stability of some selected catalysts was investigated and illustrated.     

Ni/Pillared Clays as Catalysts for the Selective Catalytic Reduction of Nitrogen Oxides by Propene

Different and alternative methods for the preparation of Ni/pillared clays based on impregnation and encapsulation procedures are reported. Several nickel precursors and metal loadings are considered in order to evaluate their influence on the structural, textural and catalytic properties of the resulting solids. The behaviour of the optimum solids as catalysts has been proved in the selective catalytic reduction of nitrogen oxides with propene, and the relevance of the oxidant nature was checked by changing the composition of the oxidant mixture. Of all the factors studied, the nature of the nickel precursors appears as the most important one, owing to the formation of different active nickel species during the synthesis procedure.     

Rate-determining Step of Selective Catalytic Reduction of NO by Acetylene Over HZSM-5

Nitrate species is crucial intermediate of selective catalytic reduction of NO by acetylene (C₂H₂-SCR) over HZSM-5. It is proposed that formation of nitrate species on the zeolite is rate-determining step of C₂H₂-SCR. The proposition is supported by the experimental results: (1) No nitrate species could be detected by in situ FTIR in steady C₂H₂-SCR over HZSM-5 at 350 °C, while the bands due to nitrate species were clearly observed on the zeolite both in situ in NO + O₂ and after a brief evacuation at the temperature; (2) Yttrium incorporation into HZSM-5 zeolite considerably enhanced nitrate species formation on the catalyst and correspondingly the activity of the catalyst for C₂H₂-SCR was significantly increased. Both the promotional effect of yttrium on C₂H₂-SCR and the rate-determining step of C₂H₂-SCR being nitrate species formation over the catalyst were first reported herein.     

The Selective Catalytic Reduction of NO by Hydrocarbons over Pt- and Ir-Based Catalysts

Platinum- and iridium-based catalysts are the most active ones among noble metals for the selective catalytic reduction of NO by hydrocarbons (HC-SCR). Yet, the level of our understanding of the behavior of these two metals varies greatly. From the early stages of the research efforts in the HC-SCR field Pt-based catalysts were identified as “promising” and have been studied extensively for this application. Subsequently, there is a substantial body of literature focusing on the catalytic performance of such systems, as well as on the fundamental chemistry taking place on their surface under HC-SCR conditions. A fairly good understanding of the behavior of such catalysts has been developed and different reaction mechanisms have been proposed and debated extensively. In contrast, limited information is available regarding the properties and HC-SCR behavior of Ir-based catalysts. Recent reports have demonstrated advantages in the HC-SCR performance of such catalysts and have documented substantial iridium particle size, support and promoter effects.