The hydroformylation reaction can catalyze the conversion of olefins into aldehydes under the atmosphere of carbon monoxide and hydrogen, which is an important pathway for the high value-added conversion and utilization of olefins. More than 10 million tons of olefins worldwide undergo high-value conversion through this reaction pathway every year, making it one of the largest homogeneous catalytic processes currently available. Among them, rhodium catalyzed propylene hydroformylation accounts for over 70% of the total production capacity of olefin hydroformylation. The product of this process, n-butanal, is usually further converted into n-butanol and 2-ethylhexanol. The two are basic chemical raw materials for the production of plasticizers, detergents, coatings, and pharmaceuticals in bulk daily necessities. However, the rhodium molecular catalyst is in the same phase as the raw materials and products, so the separation and recycling of the catalyst after the reaction is accompanied by the loss of rhodium. A study has proposed the idea of developing reusable supported multiphase catalysts to reduce the loss of rhodium metal. Meanwhile, due to the lack of a ligand environment similar to that of homogeneous catalysts, it is generally believed that the catalytic active center of supported catalysts is a freely rotating species of "dicarbonyl rhodium hydrogen" that is not affected by steric effects, and the regioselectivity for generating higher value-added n-butanal in hydroformylation reactions is poor. This is a challenge facing the practical application of multiphase supported hydroformylation catalysts.
Recently, Cao Zhi, a researcher of Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, cooperated with China Science Synthetic Oil Technology Co., Ltd. to realize hydroformylation of propylene to produce n-butyraldehyde with ultra-high regioselectivity for the first time by using a heterogeneous "rhodium molecular sieve" supported catalytic system. The team extended the classic shape selection effect of molecular sieve skeletons on reaction intermediates and applied it to the narrow confinement space formed between molecular sieve skeletons and structurally clear rhodium active sites. By inhibiting the generation of isobutyraldehyde intermediates with significant steric hindrance in the hydroformylation reaction, they achieved a regional selectivity of over 99% for the target product n-butyraldehyde, with a total selectivity of over 99% for aldehyde products and a catalyst conversion frequency of over 6500 h-1. The above catalytic performance results exceed all reported heterogeneous catalysts and almost all homogeneous catalysts so far.
This study provides a new method for selectively obtaining thermodynamically more unstable anti maleic addition products, namely n-butanal, using multiphase catalysis. It expands the concept of classical molecular sieve framework "shape selective catalysis" and provides new solutions and methods for the challenges in the industrial production of propylene hydroformylation.
On April 24th, the relevant research results were published in Nature. The research work has received support from the National Key R&D Program, the National Natural Science Foundation of China, and the Research Fund of China Science and Technology Corporation for Synthetic Oil.
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