Abstract
Homogeneous molecular catalysts and heterogeneous catalysts possess complementary strengths, and are of great importance in laboratory/commercial procedures. While various porous hosts, such as polymers, carbons, silica, metal oxides and zeolites, have been used in an attempt to heterogenize homogeneous catalysts, realizing the integration of both functions at the expense of discounting their respective advantages, it remains a significant challenge to truly combine their intrinsic strengths in a single catalyst without compromise. Here, we describe a general template-assisted approach to incorporating soluble molecular catalysts into the hollow porous capsule, which prevents their leaching due to the absence of large intergranular space. In the resultant yolk (soluble)–shell (crystalline) capsules, the soluble yolks can perform their intrinsic activity in a mimetic homogeneous environment, and the crystalline porous shells endow the former with selective permeability, substrate enrichment, size-selective and heterogeneous cascade catalysis, beyond the integration of the respective advantages of homogeneous and heterogeneous catalysts.
Highlights
Molecular catalysts are of great importance in both laboratory and commercial procedures due to their high activity and selectivity toward many reactions
The layered double hydroxides (LDHs) with unsaturated metal sites featuring positively charged scaffolds are recognized as ideal templates for the directed growth of metal–organic frameworks (MOFs) [45,46,47]
A methanol solution of 2-methylimidazole and Zn(NO3)2·6H2O was added to the H-LDH solution at room temperature for ZIF-8 assembly onto H-LDH to yield H-LDH@ZIF-8 with a hollow structure
Summary
Molecular catalysts are of great importance in both laboratory and commercial procedures due to their high activity and selectivity toward many reactions These homogeneous catalysts suffer from intrinsic difficulty in separation/reuse and the tendency toward degradation or aggregation [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]. While the use of porous inorganic solids such as zeolites has been attempted, their microporous structures are limited to the encapsulation of small guest species and readily cause mass transfer resistance [8,9,10] Their preparation usually requires special templates (such as hard/soft templates or structure-directing agents) to create pores and subsequent high-temperature calcination to remove the templates, which is unfavorable to the encapsulation of soluble active species [8,9,10].
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