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.

In this paper, TiO2 prepared with an aqueous sol-gel synthesis by peptization process is doped with nitrogen precursor to extend its activity towards the visible region. Three N-precursors are used: urea, ethylenediamine and triethylamine. Different molar N/Ti ratios are tested and the synthesis is adapted for each dopant. For urea- and trimethylamine-doped samples, anatase-brookite TiO2 nanoparticles of 6–8 nm are formed, with a specific surface area between 200 and 275 m2·g−1. In ethylenediamine-doped samples, the formation of rutile phase is observed, and TiO2 nanoparticles of 6–8 nm with a specific surface area between 185 and 240 m2·g−1 are obtained. X-ray photoelectron spectroscopy (XPS) and diffuse reflectance measurements show the incorporation of nitrogen in TiO2 materials through Ti–O–N bonds allowing light absorption in the visible region. Photocatalytic tests on the remediation of water polluted with p-nitrophenol show a marked improvement for all doped catalysts under visible light. The optimum doping, taking into account cost, activity and ease of synthesis, is up-scaled to a volume of 5 L and compared to commercial Degussa P25 material. This up-scaled sample shows similar properties compared to the lab-scale sample, i.e., a photoactivity 4 times higher than commercial P25.

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Supported palladium nanoparticles with different diameters were synthesized by the water-in-oil microemulsion method using TiO2 as support. The materials were characterized by different physicochemical methods such as X-ray photoelectron spectroscopy (XPS), inductively coupled plasma atomic emission spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and H2 chemisorption. The results confirmed that the microemulsion method permits well-dispersed palladium nanoparticles to be obtained. The size of the nanoparticles was estimated by XPS intensity ratios using models proposed by Davis and by Kerkhof and Moulijn and compared with XRD, TEM, and H2 chemisorption analysis. Good accordance of the two models was found for very small Pd particles (smaller than 3 nm). The Kerkhof−Moulijn model seemed to be very sensitive to the small variation in the particle size distribution. The Davis model seemed to be more adequate to determine the size of small and biggest particles as compared with the Kerkhof−Moulijn model. A good accordance between TEM results and the Davis model was found. The results obtained using the Davis model permitted also understanding of the differences observed between XRD and TEM studies. XPS analysis could be a good and probably more accessible alternative to determine rapidly and with high accuracy nanosize particles of materials, in particular when others physicochemical techniques are not accessible or have a limited resolution.

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