Exploring, Tuning, and Exploiting the Basicity of Hydrotalcites for Applications in Heterogeneous Catalysis

Abstract

Basic catalysis! The basic properties of hydrotalcites (see picture) make them attractive for numerous catalytic applications. Probing the basicity of the catalysts is crucial to understand the base-catalysed processes and to optimise the catalyst preparation. Various parameters can be employed to tune the basic properties of hydrotalcite-based catalysts towards the basicity demanded by each target chemical reaction.Hydrotalcites offer unique basic properties that make them very attractive for catalytic applications. It is of primary interest to make use of accurate tools for probing the basicity of hydrotalcite-based catalysts for the purpose of 1) fundamental understanding of base-catalysed processes with hydrotalcites and 2) optimisation of the catalytic performance achieved in reactions of industrial interest. Techniques based on probe molecules, titration techniques and test reactions along with physicochemical characterisation are overviewed in the first part of this review. The aim is to provide the tools for understanding how series of parameters involved in the preparation of hydrotalcite-based catalytic materials can be employed to control and adapt the basic properties of the catalyst towards the basicity demanded by each target chemical reaction. An overview of recent and significant achievements in that perspective is presented in the second part of the paper.

Catalytic activity of hydrotalcite-derived catalysts in the dry reforming of methane: on the effect of Ce promotion and feed gas composition

“…A similar effect was observed for HTNi25-Ce catalyst, as reported in our previous work [41]. It was observed, however, that the decrease of total basicity was compensated by the increase in the concentration of intermediate and strong basic sites, which are associated with Lewis acid-base metal-oxygen pairs and low coordinated oxygen anions (strong basic Lewis sites), respectively [40,42,43].…”

“…specific surface area, S BET , total pore volume, V tot , and mean pore diameter, d p , calculated from the N 2 adsorption isotherms for different HT-derived catalysts promoted with Ce are compared with the unpromoted catalysts in Table 4. All values of textural parameters are typical for mesoporous hydrotalcite-derived mixed oxides [34,39,40]. The Ce doping did not significantly change the textural properties, since for Ce-promoted materials were at a similar level as for the parental ones, with the exception of the sample loaded with the lowest amount of Ni.…”

Glycerol Hydrogenolysis over Co Catalysts Derived from a Layered Double Hydroxide Precursor

“…Figure 1 shows the XRD patterns for the precursor, the oxide, and the Co-T samples. For the LDH precursor, the characteristic diffraction lines in the (003), (006), (012), (015), (110) and (113) planes reflected the hydrotalcite-like structure [19]. The very weak diffraction lines at 2h = 31.8°and 36.3°may be assigned to small ZnO phase (JCPDS 89-1397).…”

“…The very weak diffraction lines at 2h = 31.8°and 36.3°may be assigned to small ZnO phase (JCPDS 89-1397). The formation of a layered double hydroxide usually requires a ratio of divalent to trivalent cations in the range of 2 to 4 [19] Figure 2 shows the TEM images for the LDH, the oxide, and the Co-T samples. The LDH possessed an irregular platelet shape with an average size of 80 nm.…”

Graphene-oxide-supported CuAl and CoAl layered double hydroxides as enhanced catalysts for carbon-carbon coupling via Ullmann reaction

“…In particular, LDHs have been intensively investigated in recent years as catalysts and catalyst supports [4,5] in many aspects, such as organic synthesis, (photo) degradation of organic wastes, greenhouse gas control emission and H2 production [6][7][8][9][10][11][12][13].…”