Laboratory for Materials and Structures, Institute of Innovative Research, Tokyo Institute of Technology, Nagatsuta-cho 4259, Midori-ku, Yokohama 226-8503, Japan.
Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
ACS Appl Mater Interfaces. 2023 Apr 12;15(14):17957-17968. doi: 10.1021/acsami.3c01629. Epub 2023 Apr 3.
The development of effective solid acid-base bifunctional catalysts remains a challenge because of the difficulty associated with designing and controlling their active sites. In the present study, highly pure perovskite oxide nanoparticles with -transition-metal cations such as Ti, Zr, and Nb as -site elements were successfully synthesized by a sol-gel method using dicarboxylic acids. Moreover, the specific surface area of SrTiO was increased to 46 m g by a simple procedure of changing the atmosphere from N to air during calcination of an amorphous precursor. The resultant SrTiO nanoparticles showed the highest catalytic activity for the cyanosilylation of acetophenone with trimethylsilyl cyanide (TMSCN) among the tested catalysts not subjected to a thermal pretreatment. Various aromatic and aliphatic carbonyl compounds were efficiently converted to the corresponding cyanohydrin silyl ethers in good-to-excellent yields. The present system was applicable to a larger-scale reaction of acetophenone with TMSCN (10 mmol scale), in which 2.06 g of the analytically pure corresponding product was isolated. In this case, the reaction rate was 8.4 mmol g min, which is the highest rate among those reported for heterogeneous catalyst systems that do not involve a pretreatment. Mechanistic studies, including studies of the catalyst effect, Fourier transform infrared spectroscopy, and temperature-programmed desorption measurements using probe molecules such as pyridine, acetophenone, CO, and CHCl, and the poisoning effect of pyridine and acetic acid toward the cyanosilylation, revealed that moderate-strength acid and base sites present in moderate amounts on SrTiO most likely enable SrTiO to act as a bifunctional acid-base solid catalyst through cooperative activation of carbonyl compounds and TMSCN. This bifunctional catalysis through SrTiO resulted in high catalytic performance even without a heat pretreatment, in sharp contrast to the performance of basic MgO and acidic TiO catalysts.
具有 -过渡金属阳离子（如 Ti、Zr 和 Nb）作为 -位元素的高效固体酸碱双功能催化剂的开发仍然是一个挑战，因为设计和控制其活性位具有一定难度。在本研究中，通过使用二羧酸的溶胶-凝胶法成功合成了具有 -过渡金属阳离子（如 Ti、Zr 和 Nb）作为 -位元素的高纯钙钛矿氧化物纳米粒子。此外，通过在无定型前体煅烧过程中将气氛从 N 更改为空气，SrTiO 的比表面积从 46 m g 增加到 46 m g。所得 SrTiO 纳米粒子在未经热预处理的测试催化剂中对苯乙酮与三甲基硅氰化物（TMSCN）的氰硅烷化反应表现出最高的催化活性。各种芳香族和脂肪族羰基化合物均以良好至优异的收率有效地转化为相应的氰醇硅醚。该体系适用于苯乙酮与 TMSCN 的较大规模反应（10 mmol 规模），其中分离出 2.06 g 分析纯的相应产物。在这种情况下，反应速率为 8.4 mmol g min，是未进行预处理的多相催化剂体系中报道的最高速率。包括催化剂效应、傅里叶变换红外光谱和使用吡啶、苯乙酮、CO 和 CHCl 等探针分子的程序升温脱附测量的机理研究，以及吡啶和乙酸对氰硅烷化的毒害作用表明，SrTiO 上存在的适度强度的酸和碱位可能通过协同激活羰基化合物和 TMSCN 使 SrTiO 充当双功能酸碱固体催化剂。这种通过 SrTiO 的双功能催化作用即使没有热预处理也能实现高催化性能，与碱性 MgO 和酸性 TiO 催化剂的性能形成鲜明对比。
