Angelw. Chem. Int. ed.: ALD technology used in Shanxi coal chemical industry realizes heterogeneous homogeneous catalyst

Metal complex catalysts, especially chiral homogeneous catalysts, are very important for the development of chemical, biological and pharmaceutical industries However, these homogeneous catalysts often have the problems of difficult recovery of catalyst and difficult separation of products, which make the application cost higher, and the catalyst remaining in the product will also produce environmental and product quality problems that can not be ignored It is an important way to separate and reuse homogeneous catalysts effectively by immobilizing them to obtain heterogeneous catalysts Compared with the traditional covalent supported heterogeneous catalysts, the nanoreactor constructed by the non covalent encapsulation of homogeneous catalysts into mesoporous or mesoporous molecular sieves can maintain the degree of freedom and activity of chiral complexes Qin Yong, a research team from the State Key Laboratory of coal transformation, Shanxi Institute of coal and chemical technology, Chinese Academy of Sciences, put forward a universal method to realize heterogeneous catalyst using diffusion limited atomic layer deposition (ALD) technology This method constructs a hollow rivet structure by selectively depositing metal oxides on the pore of mesoporous molecular sieve The pore size of the pore can be precisely adjusted from nanometer level to molecular level It can be applied to the physical encapsulation of various homogeneous catalysts in the pore After encapsulation, the homogeneous catalyst can maintain or improve the activity and chiral catalytic selectivity of the homogeneous catalyst, and has super high repetition Usability ALD is an advanced thin film deposition technology, which has a good application prospect in the precise design of catalyst structure On the basis of rich ALD deposition experience and catalyst structure design in the early stage, the research team applied the diffusion rule of precursor in porous material channel during ALD process to encapsulate homogeneous catalyst in mesoporous material channel a) The preparation process of encapsulated catalyst; b) the pore size decreases with the increase of ALD cycle number; c) the deposition depth of metal oxide increases with the increase of precursor diffusion time (source: angel Chem Int ed.) take the CO (salen) as an example Firstly, CO (salen) was impregnated into the nano tube by vacuum impregnation Then, titanium tetraisopropanol (tip) and H 2O were used as ALD precursors to selectively deposit TiO 2 near the orifices to form rivets with holes By controlling the number of deposition cycles of TiO2, the SBA-15 pore size can be adjusted below the catalyst molecular size (0.8 nm), thus realizing the encapsulation of metal complexes By changing the pulse time (diffusion time) of tip, the deposition depth of TiO2 in the channel can be controlled, thus the length of rivet can be changed a) The activity and stability of MTiO 2-1.5/co (salen) / SBA-15 encapsulation catalyst increased with the increase of TiO2 cycle number m, and M = 200 reached the optimum; B-C) 200tio 2-1.5/co (salen) / SBA-15 encapsulation catalyst pore size decreased from 9.2nm to 0.8nm; d) cross section samples were prepared by focused particle beam, and stem analysis revealed that the depth of rivet structure was 1.1 μ m (source: angel Chem Int Ed.) used CO (salen) to catalyze the asymmetric hydrolysis and resolution of propylene oxide as a probe reaction When the pulse time was fixed to 1.5 s, the number of ALD cycles was changed to control the size of the orifice At 200 cycles, the catalyst obtained the optimal activity, enantioselectivity and reusability (200tio2-1.5 / CO (salen) / SBA-15) After 8 times of reusing, it still maintained high performance The results showed that the pore size of the catalyst orifice decreased to 0.8 nm and the diffusion depth of rivet structure was 1.1 μ M The pulse (diffusion) time corresponds to the deposition depth of ALD With the increase of pulse time from 0.5 s to 8.5 s, the deposition depth of TiO2 in SBA-15 increases from 550 nm to 5.5 μ M In this way, according to the length of the pore channel, a suitable short diffusion time can be selected to achieve the encapsulation of the complex molecules A shorter diffusion time can obtain a larger space to encapsulate the complex molecules and obtain a higher catalytic activity This method provides a more simple and accurate method for heterogeneous catalyst The method has good universality and can be applied to the encapsulation of various complexes (CO (salen), [(salen) Ti (μ - O)] 2, etc.) in various mesoporous molecular sieve channels (SBA-15, MCM-41, SBA-16, etc.), and the encapsulation can be realized by simply adjusting the process according to the size of the complexes and molecular sieve pore diameter, so as to obtain a reusable and efficient catalyst Paper link: http://onlinelibrary.willey.com/doi/10.1002/anie.201712010/full corresponding author: Qin Yong http://people.ucas.ac.cn/ ~ qnyong