Design of High-Performance Heterogeneous Metal Catalysts for Green and Sustainable Chemistry

Abstract

This account reviews a novel approach to designing high-performance heterogeneous metal catalysts using hydroxyapatites, montmorillonites, and hydrotalcites as macroligands of active metal species for aerobic alcohol oxidations, carbon-carbon bond formations, and one-pot syntheses. The catalytic systems using the above heterogeneous catalysts offer significant benefits in achieving environmentally friendly organic syntheses aiming towards Green and Sustainable Chemistry. Furthermore, the present preparation method for the immobilization of metal species is strikingly simple and allows a strong protocol for creating various nanostructured and functionalized heterogeneous catalysts.Green and Sustainable Chemistry (GSC) is a revolutionary philosophy that aims to bring about a sustainable society by improvement of the safety and environmental aspects of chemical processes and reduction of the risks of chemical products to people and the environment.1 The emphasis is on eliminating waste at the source-primary pollution prevention-rather than finding incremental end-of-pipe solutions. This concept aims to solve the societal problems of the last century associated with the mass production and consumption of materials, and plays a prime role in providing a venous function in society, encouraging reuse and circulation of resources.One of the powerful solutions in the move toward GSC is the replacement of traditional synthetic methods using harmful stoichiometric reagents that produce vast amounts of waste with cleaner and simple catalytic alternatives with high atom efficiency 1a and low E-factors. 1b Catalytic chemistry, therefore, is of ever-increasing importance because catalysis is a key element in material transformations at atomic and molecular levels, which are an essential realm of chemistry and chemical processes.Our approach to GSC is to develop a highly functionalized heterogeneous metal catalyst based on the unique characteristics of natural layered inorganic materials such as hydroxyapatite, montmorillonite, and hydrotalcite, by using them as macroligands for metal species.2 We consider the above inorganic materials to be advanced nano-scaled catalyst supports allowing for the control of the location of catalytically active metal species, which can be found, for example, on the surface, among the layers, or in the interlayer space. Furthermore, these materials are capable of creating catalytically active metal species responsible for targeted organic transformations involving monomers, chain-like species or giant clusters. The creation of well-defined active metal sites on a solid surface, as characterized by X-ray absorption spectroscopy, not only opens up an avenue to materials that boost catalytic performance, but also aids in the understanding of the molecular basis of heterogeneous catalysis. Another advantage of these catalysts is the possibility of a one-pot synthesis based on a cooperative action by several immobilized active species on the solid surface as multifunctional catalysts. The target react...

Click chemistry from organic halides, diazonium salts and anilines in water catalysed by copper nanoparticles on activated carbon

“…In this sense, it is important to unveil the nature of the catalysis, with heterogeneous catalysis by supported metals being advantageous over the homogeneous counterpart. 27 For this purpose, benzyl bromide (1a) and phenylacetylene (2a) were reacted up to a >99% conversion (<3 h) (Scheme 1). Then, the resulting mixture containing the triazole 3aa was subjected to additional heating, until a total time of 24 h, in order to force any possible copper leaching.…”

CuII(Sal-Ala)/CuAlLDH Hybrid as Novel Efficient Catalyst for Artificial Superoxide Dismutase (SOD) and Cyclohexene Oxidation by H2O2

“…The TG profile of CuAlLDH shows four stages of weight loss as previously studies revealed [44]. The first step corresponds to the removal of physically adsorbed and intergallery water and some loosely bound CO 3 2-(45-160°C, 6.80 % weight loss), then the second step corresponds to the loss of structural water and CO 3 2-(160-300°C, 12.50 % weight loss). The third weight loss (300-675°C, 6.70 % weight loss) is due to some strongly held carbonate anions.…”

“…One approach is the immobilization of the metal catalyst into inorganic supports [3]. Another one is the use of the inorganic crystallites (hydroxyapatites, montmorillonites, hydrotalcites) as macroligands of the active species, allowing the development of highly functionalized heterogeneous metal catalysts that show the concerto effects between the active metal species and surface properties of the support [3,4].…”

“…Hence, in recent years, a sustained research was carried out to develop novel heterogeneous oxidation catalysts [1,3,[14][15][16]. Schiff base complexes containing donor atoms such as oxygen and nitrogen were immobilized into different supports and have been used for oxidation reactions [17][18][19][20][21].…”

Pictet-Spengler condensation reactions catalyzed by a recyclable H+-montmorillonite as a heterogeneous Brønsted acid

“…By replacing the sodium cation in the interlayer space, various types of metal cations and protons can be readily introduced into the interlayer of the mont. Thus montmorillonite clays, in its cation-exchanged forms, possess both Lewis and Brønsted acidities and can be used as heterogeneous acid catalysts in organic synthesis, with advantages such as thermal stability, effective activity, high selectivity, less waste production, and an improved recuperation of immobilized catalysts [4][5][6].…”