Department of Chemistry and Biochemistry, Kent State University , Kent, Ohio 44240, United States.
Department of Chemical Engineering, Federal University of Sao Carlos , Sao Carlos, Sao Paulo13565-905, Brazil.
ACS Appl Mater Interfaces. 2017 Feb 22;9(7):6079-6092. doi: 10.1021/acsami.6b15507. Epub 2017 Feb 8.
One-pot synthesis of nanostructured ternary oxides of Ni, Al, and Ti was designed and performed via evaporation induced self-assembly (EISA). For the purpose of comparison, analogous oxides were also prepared by the impregnation method. The resulting materials were applied in two catalytic reactions: steam reforming of ethanol (SRE) for H production (subjected to prior activation with H) and ethanol dehydration (ED; used without prior activation), to in situ analyze carbon accumulation by ethylene depletion when ethanol interacts with acidic sites present on the support. Modification of Ni-Al mixed oxides with titania was shown to have several benefits. CO, NH, and propylamine sorption data indicate a decrease in the strength of acidic and basic sites after addition of titania, which in turn slowed down the carbon accumulation during the ED reaction. These changes in interactions between ethanol and byproducts with the support led to different reaction pathways in SRE, indicating that the catalysts obtained by EISA with titania addition showed higher ethylene selectivity and CO/CO ratios. The opposite was observed for the impregnated catalysts, which were less coke-stable during ED reactions and showed no ethylene selectivity in SRE. Carbon formed during ED reactions was shown to be thermodynamically less favorable and easier to decompose in the presence of titania. All catalysts studied displayed similar and high selectivities (∼80%) and yields (∼5.3 mol/mol) toward H, which place them among the most active and selective catalysts for SRE. These results indicate the importance of tailoring the support surface acidity to achieve high reforming performance and higher selectivity toward SRE, one of the key processes to produce cleaner and efficient fuels. For an efficient reforming process, the yield of byproducts is low but still they affect the catalyst stability in the long-run, thus this work may impact future studies toward development of near-zero coke catalysts.
通过蒸发诱导自组装（EISA）设计并进行了 Ni、Al 和 Ti 的纳米结构三元氧化物的一锅合成。为了进行比较，还通过浸渍法制备了类似的氧化物。将所得材料应用于两种催化反应中：用于 H2 生产的乙醇蒸汽重整（在 H2 存在下进行预先活化）和乙醇脱水（ED；在没有预先活化的情况下使用），以原位分析乙醇与载体上存在的酸性位相互作用时碳的积累情况。用 TiO2 改性 Ni-Al 混合氧化物具有多种益处。CO、NH3 和丙胺吸附数据表明，添加 TiO2 后，酸性和碱性位的强度降低，从而在 ED 反应中减缓了碳的积累。这改变了乙醇和副产物与载体之间的相互作用，导致 SRE 中的反应途径不同，表明添加 TiO2 的 EISA 获得的催化剂表现出更高的乙烯选择性和 CO/CO 比。浸渍催化剂则相反，它们在 ED 反应中不太稳定且在 SRE 中没有乙烯选择性。ED 反应中形成的碳被证明在热力学上不太有利，并且在存在 TiO2 的情况下更容易分解。所有研究的催化剂在 ED 反应中均显示出类似的高选择性（约 80%）和产率（约 5.3 mol/mol），对 H2 具有较高的选择性，这使它们成为 SRE 中最活跃和选择性最高的催化剂之一。这些结果表明，调节载体表面酸性以实现高效重整性能和对 SRE 更高的选择性非常重要，SRE 是生产清洁高效燃料的关键过程之一。对于有效的重整过程，副产物的产率较低，但仍会影响催化剂的长期稳定性，因此这项工作可能会影响未来对开发近零积碳催化剂的研究。
