焦油水蒸气重整镍基合金催化剂的可控制备及性能研究

Biomass gasification is one of the most promising technologies for the conversion and utilization of biomass energy. However, the formation of tar by-products during biomass gasification is among the main obstacles preventing commercialization of this technology. Catalytic steam reforming of tar is considered as the most effective approach for tar removal and the key is to develop cost-effective and efficient reforming catalysts. Nickel-based alloy catalysts are shown to exhibit good performance for the steam reforming of tar, and superior performance can be expected by carefully controlling the structure, composition, and particle size of the alloy particles. In this research, we attempt to prepare a high-performance Ni-based alloy catalyst by using layered double hydroxides (LDHs) as precursor. Based on the unique properties of LDHs, Ni and other transition metal-substituted Mg-Al LDHs precursors would be synthesized, followed by calcination and reduction treatments. By confining the chemical compositions and heat treatment conditions of the LDHs precursors, highly dispersed alloy nanoparticles with identical crystalline structure as well as homogeneous composition and particle size would be obtained. A detail characterization of the alloy catalysts would be performed to get information about the structural and physicochemical properties of the alloy nanoparticles, including the morphology, crystalline phase, composition, metal dispersion, microstructure, surface state, and so on. Also, a systematic study on the catalytic activity, stability, and reaction kinetics of the alloy catalysts in the steam reforming of tar model compounds would be carried out, with an aim to get insight into the superior catalytic behavior of the alloy nanoparticles as well as the key factors that influence their catalytic performances. Based on the results of structural characterization and catalytic tests, the role of alloying in determing the catalytic performance would be carefully discussed in order to reveal the relationship between the alloy structure and the catalytic activity, and to understand the promoting effect of alloying in the inhibition of the catalyst deactivation caused by coke deposition, sintering, and sulfur poisoning. It is expected that the findings in this research would provide useful information for understanding the synergetic catalysis on alloys and would be helpful for the design and synthesis of novel catalysts with excellent performance for the steam reforming of tar as well as their application in biomass gasification.

生物质气化是生物质能转化和利用的关键技术之一，制约生物质气化技术发展的技术瓶颈之一是焦油副产物的有效去除，焦油水蒸气催化重整是解决焦油问题最有效的方法，Ni与其他过渡金属形成的合金催化剂对焦油水蒸气重整反应呈现良好的催化性能，通过合金组成、结构和形貌的调控是改善合金催化剂性能的关键。本项目拟以层状复合氢氧化物（LDHs）为前驱体制备高性能Ni基合金催化剂，通过调控LDHs前驱体的化学组成及热处理条件，研制组成均匀、结构单一、粒径均一的高性能实用型合金催化剂，通过合金组成、晶相、微结构、表面状态等性质的系统表征，结合催化剂活性、稳定性及反应动力学研究，确定影响合金催化性能的关键因素，发展合金催化剂的性能调控方法，揭示合金化对催化剂积碳、烧结和硫中毒失活的抑制作用，为新型高效焦油水蒸气重整催化剂的研发提供理论基础和原型技术。

焦油重整是解决生物质气化中焦油副产物的最有效方法，其关键是研制廉价、高性能的催化剂。本项目采用层状复合氢氧化物（LDHs）为前驱体设计制备了系列高分散负载型金属/合金催化剂，通过XRD、H2-TPR、O2-TPO、XPS、H2化学吸附、CO吸附红外光谱、STEM-EDX、TPSR等手段对催化剂进行表征，并以焦油模型化合物为反应物详细考察了催化剂对焦油重整的活性、稳定性和反应动力学。研究结果表明：（1）以LDHs为前驱体是制备负载型金属和合金催化剂的有效方法。过渡金属离子部分取代Mg-Al LDHs经焙烧分解后形成了类Mg(Al)O固溶体，经还原处理后可得到高分散的金属纳米粒子（如Ni、Co、Cu）和结构单一、组成均匀、粒径均一的合金纳米粒子（如Ni-Cu、Ni-Fe、Ni-Co等）。该方法克服了传统浸渍法存在的多相合金并存、组成不均匀、粒径较大且分布较宽等问题，实现了合金催化剂的可控制备。（2）合金催化剂对焦油模型化合物重整反应表现出良好的催化活性、稳定性和抗积碳性能。研究发现，合金的种类和组成对催化性能有显著影响。其中，Cu/Ni比为0.25的Ni-Cu/Mg(Al)O合金催化剂对甲基萘水蒸气重整和甲烷二氧化碳重整均表现出较好的催化活性和稳定性，是目前已报道的最有效的非贵金属催化剂之一。此外，研究发现以Co-Mg-Al LDHs为前驱体制备的Co/Mg(Al)O催化剂具有优异的低温催化稳定性和抗积碳性能。（3）合金可有效抑制积碳生成。TPSR和动力学研究显示，合金化可降低甲烷等烃类分子的解离，并促进H2O、CO2等分子的吸附活化，加快表面碳物种的气化，从而抑制积碳生成。这些研究结果对发展合金催化剂的制备和性能调控方法以及认识合金对积碳的抑制作用具有重要意义，将为新型高效烃类重整催化剂的研发提供理论基础和原型技术。