Generation of Basic Centers in High-Silica Zeolites and their Application in Gas-Phase Upgrading of Bio-Oil
Generation of Basic Centers in High-Silica Zeolites and their Application in Gas-Phase Upgrading of Bio-Oil
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DOI：
10.1002/cssc.201301382
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发表时间：
2014-06-01
期刊：
影响因子：
8.4
通讯作者：
Perez-Ramirez, Javier
中科院分区：
文献类型：
--
作者：
Keller, Tobias C.;Rodrigues, Elodie G.;Perez-Ramirez, Javier
高硅沸石作为液相和气相缩合反应的有效催化剂最近已被报道，因为与富铝碱性沸石相比，存在碱性的补充来源。在此，我们描述了富硅FAU、NH4和MFI沸石上这些活性位点的受控生成。通过在Na2CO3水溶液中应用温和的碱处理，在沸石内产生碱金属配位缺陷，而完全保留多孔性质。将所得催化剂应用于丙醛在673 K下的气相缩合反应中作为热解油催化改质的模型反应，与未改性的沸石相比，其活性提高了20倍。这些新位点的中等碱性导致比传统碱催化剂如CsX和MgO优越的抗结焦性上级，并且对于缩合途径实现了相当的活性和优异的选择性。通过战略性的酸和碱处理和魔角旋转NMR光谱的使用，活性中心的性质进行了研究，这支持了硅氧基作为基本中心的理论。这一贡献是理解和设计高硅基催化剂的关键一步，用于在生产第二代生物燃料的加氢处理步骤之前对粗生物油进行中间脱氧。
High-silica zeolites have been reported recently as efficient catalysts for liquid- and gas-phase condensation reactions because of the presence of a complementary source of basicity compared to Al-rich basic zeolites. Herein, we describe the controlled generation of these active sites on silica-rich FAU, BEA, and MFI zeolites. Through the application of a mild base treatment in aqueous Na2CO3, alkali-metal-coordinating defects are generated within the zeolite whereas the porous properties are fully preserved. The resulting catalysts were applied in the gas-phase condensation of propanal at 673K as a model reaction for the catalytic upgrading of pyrolysis oil, for which an up to 20-fold increased activity compared to the unmodified zeolites was attained. The moderate basicity of these new sites leads to a coke resistance superior to traditional base catalysts such as CsX and MgO, and comparable activity and excellent selectivity is achieved for the condensation pathways. Through strategic acid and base treatments and the use of magic-angle spinning NMR spectroscopy, the nature of the active sites was investigated, which supports the theory of siloxy sites as basic centers. This contribution represents a key step in the understanding and design of high-silica base catalysts for the intermediate deoxygenation of crude bio-oil prior to the hydrotreating step for the production of second-generation biofuels.