Long-chain polyphosphates can bridge clay particles leading to new arrested systems: all-inorganic aqueous Wigner glasses. These materials may have use in agriculture and health sciences.

Mixed oxides were obtained via calcination at 550 °C from layered double hydroxides (LDHs), which were synthesized in a previous study via co-precipitation and co-precipitation followed by hydrothermal treatment using aluminum residues as the source of this element. After characterization, these oxides (Mg-Al-_LDH-CP and Mg-Al-_LDH-H, named according to the synthesis methods of the precursor LDHs) were applied as heterogeneous catalysts in the methyl transesterification of ethyl acetate (EA). The formation of mixed oxides was confirmed by the absence of basal peaks associated with the layered LDH structure in the XRD analysis, due to calcination. Further characterization revealed that Mg-Al-_LDH-CP exhibited the highest number of acidic sites, while Mg-Al-_LDH-H had the highest number of basic sites. The transesterification activity was evaluated in the reaction between ethyl acetate (EA) and methanol (MeOH). The best result, obtained under a molar ratio of 1:5:0.005 (EA:MeOH:catalyst) at 120 °C, was a 63% conversion after 360 min of reaction for the Mg-Al-_LDH-CP catalyst, which had a higher number of acidic sites and fewer basic sites. Additionally, the catalysts demonstrated robustness, maintaining catalytic activity over four cycles without a significant decrease in performance. These results indicate the feasibility of using mixed oxides derived from LDH, synthesized from aluminum residues, as heterogeneous catalysts in transesterification reactions, highlighting their potential for advancing more sustainable catalyst development.

Catalysts were synthesized with Ni and bentonite clay, without previous treatment, through wet impregnation with 5, 10 and 20% of Ni (m/m). They were characterized by energy dispersive X-ray fluorescence spectrometry (EDX), X-ray diffraction (XRD), temperature-programmed reduction (TPR), thermogravimetric analysis (TGA), adsorption and desorption of N2 at 77 K, and transmission electron microscopy (TEM). The catalytic activity in relation to the methane conversion reaction was evaluated at 500 °C for 0.5 h. The addition of 10 and 20% of nickel to the clay led to a disordered bentonite structure, characterized by the disappearance of the 001 reflection on the X-ray diffractograms, with a consequent increase in the interaction between nickel oxide and clay (TPR). All catalysts synthesized showed catalytic activity in relation to the conversion of methane to form ordered carbon. The catalyst with 20% of nickel had the highest activity, with 74% of methane conversion.