载体表面氧化程度对Ni/SiC甲烷化催化剂性能的影响

采用等体积浸渍法制备了Ni/SiC甲烷化催化剂, 研究了SiC载体表面氧化程度对催化剂低温活性和高温稳定性的影响, 并采用热重-差示扫描量热、N₂物理吸附、傅立叶变换红外光谱、氨程序升温脱附、X射线衍射、氢程序升温还原和氢化学吸附技术对样品进行了表征. 结果表明, 随着载体氧化温度的提高, 催化剂的比表面积和镍分散度降低, 但还原性和反应稳定性提高. 未氧化载体所负载催化剂的高温稳定性最差, 其原因在于载体对镍粒子的固定作用最弱. 负载于500和700℃处理的SiC载体上的催化剂具有较好的低温活性和高温稳定性, 这是因为适度氧化后的载体能较好地分散并固定镍粒子. 900℃处理的载体因过度氧化形成了低活性的氧化层, 使负载的镍粒子变大, 因而催化剂的低温活性最差.     

二氧化碳甲烷化研究进展

本文从热力学，催化，反应机理方面评述了二氧化碳甲烷化的研究概况。     

Temperature-programmed surface reaction (TPSR) of CH4 synthesis by PdxNi100−x nanoparticles

A series of Pd_xNi_100−x nanoparticles were prepared by the co-precipitation method and analyzed using a temperature-programmed surface reaction (TPSR) of their methanation reactions. ESCA measurement suggested that the as-prepared Pd-Ni alloys had Pd-core/Ni-shell structure. Surface Pd segregation occurred during H₂ reduction and resulted in a surface composition close to the nominal value. The TPSR experiments were performed by pre-adsorption of CO with H₂ to form methane. The peak temperature of methanation increased as Pd content increased, indicating that a methanation reaction is favored on Ni and Ni-rich alloy nanoparticles. For physical mixtures of Pd and Ni nanoparticles, methanation behaviors is similar to those of alloy nanoparticles; but the methanation temperatures of physical mixtures are always higher than those of alloy nanoparticles. This may be due to the formation of a Pd-enriched alloy surface layer during reduction in H₂ at 400 °C, or because the CO molecules adsorbed on the Pd sites spill over onto the Ni sites for methanation. Using TPSR technique and measuring methanation temperature, the top-most surface of such bimetallic nanoparticles can be probed.     

Nickel deposition on γ-Al2O3 model catalysts: An experimental and theoretical investigation

Recently, surface modifications on a commercial Ni/γ-Al₂O₃ catalyst during the production of methane from synthesis gas were investigated by quasi insitu X-ray photoelectron spectroscopy (XPS) [I. Czekaj, F. Loviat, F. Raimondi, J. Wambach, S. Biollaz, A. Wokaun, Appl. Catal. A: Gen. 329 (2007) 68]. The conclusion was that the reactivity and the observed reaction mechanisms on the different Ni particles are influenced directly by both the size and the composition of the particles on the γ-Al₂O₃ support.In this investigation, Ni deposition and cluster growth on model catalyst samples (10 nm thick, polycrystalline γ-Al₂O₃ on Si(100)) were investigated by XPS. Several steps in the binding energy during Ni deposition indicate changes in the cluster growth. The molecular structure of the catalyst was investigated using Density Functional Theory calculations (StoBe) with a cluster model and non-local functional (RPBE) approach. An Al₁₅O₄₀H₃₅ cluster was selected to represent the γ-Al₂O₃(100) surface. Ni clusters of different size were cut from a Ni(100) surface and deposited on the Al₁₅O₄₀H₃₅ cluster in order to validate the deposition model determined by XPS.     

La2O3对Ni/γ-Al2O3甲烷化催化剂的助催化作用

我国将稀土作为助剂引入镍基甲烷化催化剂,大大提高了催化剂的活性和热稳定性,并已投入工业应用［1－3］．稀土对不同镍催化剂反应性能及其作用机理的研究已有一些报导［3－7］．谢有畅等观察到镍负载在经单层La2O3改性的γ－Al2O3表面,其晶粒要比没有La2O3时小得多．Rotgerink等认为添加La后反应速率的增加不只是由于几何效应,而是La对甲烷化本身有促进作用,单位镍表面的活性是随La含量不同而改变的,活性增加的同时表观活化能也增加［5］．作为助剂的La2O3在氢还原和反应过程中的变化及其作用的研究和讨论较少,目前一般认为添…     

多组分金属催化剂表面漫反射紫外可见光谱研究

研究了二氧化碳加氢甲烷化二组分、三组分担载型金属催化剂表面漫反射紫外可见光谱（ＤＲＵＶＳ）。根据ＤＲＵＶＳ提供的信息,揭示了催化剂组分间相互作用结果对催化活性的影响;不同助剂量催化剂ＤＲＵＶＳ特征强度与催化活性间定量关系也得到合理确定 。     

镍基甲烷化催化剂中的助剂作用 Ⅱ重稀土氧化物添加剂的结构效应和电子效应

应用ＢＥＴ、气相色谱、红外光谱、竞争加氢反应和ＸＰＳ等方法,在以前工作的基础上继续考察了Ｙ２Ｏ３、Ｓｍ２Ｏ３、Ｅｕ２Ｏ３、Ｇｄ２Ｏ３、Ｔｂ４Ｏ７、Ｄｙ２Ｏ３、Ｅｒ２Ｏ３、Ｔｍ２Ｏ３、Ｙｂ２Ｏ３作为添加剂,对镍在γ－Ａｌ２Ｏ３表面的分散度、甲烷化活性、ＣＯ在镍上的吸附态及表面镍原子的电子状态的影响．结果表明,稀土氧化物添加剂不仅明显地提高了金属镍的分散度和甲烷化活性,还直接地影响表面镍原子的电子状态．对不同稀土氧化物,这些效应各异．作者认为,利用稀土氧化物添加剂调节表面镍原子的电子状态,可能成为改进甲烷化催化剂活性的一个有效途径．     

Optimization of structured cellular foam-based catalysts for low-temperature carbon dioxide methanation in a platelet milli-reactor

Here, we present a preliminary study to choose a catalyst with enough catalytic activity at temperatures below 250 °C, in order to study heat transfer in a platelet milli-reactor (PMR) with an infrared camera and a commercial window inserted on the top of our reactor that only withstands a maximal temperature of 250 °C. The higher methane productivity of foam catalysts compared to powder catalysts was revealed. Foam catalysts, all impregnated with the same amount of active phase (Ni + Ru) and with different coatings, were compared to SiC only impregnated with Ni + Ru. The different coatings studied were: carbon nanofibers (CNF), ceria–zirconia (CZ) and the combination of both. Both CNF and CZ washcoats were able to increase the low specific surface area of the SiC foam. Moreover, the presence of ceria–zirconia was proven to be essential for ensuring high methane productivities. The catalyst combining both CNF and CZ showed the best results.     

二氧化碳甲烷化催化剂研究 Ⅲ.Ni-Ru-稀土/ZrO_2作用下的催化反应机理

用漫反射傅里叶红外光谱法研究了Ｎｉ－Ｒｕ－稀土／ＺｒＯ２多组分催化体系作用下的二氧化碳甲烷化反应机理．结果表明，碳酸根、甲酸根和一氧化碳是催化剂表面可以检出的吸附物种，其中表面的含氧酸根类物种是催化反应的主要中间物．二氧化碳通过与载体表面羟基的作用转化为含氧酸根类物种吸附于催化剂表面，并进一步氢解为甲烷．反应中生成的少量一氧化碳可能来源于表面含氧酸根氢解为甲烷的副反应．含不同稀土的多组分催化剂作用下的二氧化碳甲烷化过程有相同的反应机理．