Layered double hydroxides (LDHs) are often used as precursors for mixed-oxide catalysts and the deposition of a LDH layer on supporting materials would be advantageous because of better utilization of active components. The purpose of the present study was to investigate the formation of LDHs on Al2O3/Al supports prepared by the anodic oxidation of aluminum foil in dilute aqueous solutions of Co, Mn, and/or Ni nitrates. The LDH deposition was carried out under hydrothermal conditions at 80–180°C for periods ranging from 8 h to 7 days. In the initial stages of the reaction, a surface alumina hydration was observed. The LDH phase was detected after long-term deposition (3–7 days) at 120–160°C and only a small amount of Mn was incorporated in the LDHs deposited. In solutions containing only Co and Mn cations, scanning electron microscopy (SEM) images show a gradual growth of platy crystals resulting in the formation of discrete bulky aggregates with sizes up to several tens of micrometers. The adhesion of aggregates to the support probably decreased with increasing size and oversized aggregates fell away; none was found in SEM images of the samples obtained after prolonged reaction times. When Ni cations were present in the solution, they were incorporated preferentially into the LDH phase; an homogeneous layer was formed, with single platy crystals oriented perpendicular to the support. After calcination at 500°C, the products formed on Al2O3/Al support exhibited a shift of reduction maxima to higher temperatures in comparison with mixed oxides obtained by thermal decomposition of coprecipitated LDHs.

The conventional cauliflower-like shape of magadiite imposes serious limitations on its applications in adsorption, catalysis, ion exchange, etc. To overcome this problem, a method to prepare it with plate-like structures was developed. This novel approach is based on an interface-controlled heterogeneous nucleation process. Zirconia grinding balls with diameters of 2.0 mm were dispersed in the starting solution to provide solid-liquid interfaces. Then the starting solution with a SiO2:NaOH:H2O molar ratio of 9:2:75 was subjected to hydrothermal treatment at 433 K for 96 h. The presence of the solid-liquid interface improved the crystallization yield and controlled the morphology and specific surface area of the crystals. With the zirconia balls, the yield and sizes of the plate-like magadiite were 52 wt.% and 1–3 μm, respectively. In the absence of zirconia balls, the yield was smaller (45 wt.%) and magadiite shaped like cauliflower was formed. The plate-like magadiite had a specific surface area of 66 m2 g−1 and a pore-size distribution between 4 and 5 nm, compared with a surface area of 28 m2 g−1 for the cauliflower-like magadiite. In addition, the plate-like magadiite was a more effective ion exchanger than the cauliflower-like magadiite with a cation exchange capacity of 64.5 mmol/100 g (compared to 53.8 mmol/100 g for the cauliflower-like form) and it had a faster sorption rate for calcium ions.

Studies of the paragenesis of authigenic illite in arkosic sandstones of various regions and ages have revealed that the illitization of kaolinite is an important reaction accounting for the formation of authigenic illite in sandstones during burial diagenesis. The illitization of kaolinite takes place at an intermediate burial depth of 3–4 km, where pressure can reach values of 100 MPa (≈ 1000 bars). The purpose of the present study was to analyze the effect of pressure on the rate of kaolinite illitization in alkaline conditions. Hydrothermal reactions were conducted on KGa-1b kaolinite in KOH solution at 300°C and under pressures of 500, 1000, and 3000 bars for 1 to 24 h. The visual examination of the X-ray diffraction (XRD) patterns indicated a notable influence of pressure on the reaction rate. Molar percentages of muscovite/illite formed at each time interval were calculated from the analysis of two diagnostic XRD peaks, representing the 060 reflections of kaolinite and muscovite/illite. The data were modeled to obtain the initial rate of conversion at each pressure. The results indicated that the initial rate of kaolinite to muscovite/illite conversion is one order of magnitude greater at 3000 bars than at 500 or 1000 bars. Comparison of these data with those in the literature show a faster conversion rate (several orders of magnitude) in an initially high-alkaline solution than in a near-neutral solution.

The RNA world hypothesis and the hydrothermal origin of life hypothesis are contradictory to each other. Although it is considered that RNA molecules are too labile to maintain life-like systems at high temperatures and there is extensive literature on nucleic acid hydrolysis, the stability and the chemical evolution of RNA have not been sufficiently analysed from the viewpoint of hydrothermal reactions. Based on our experimental data concerning the stability and the prebiotic formation of RNA at high temperatures, two different aspects seem to be important for evaluating whether RNA molecules are too labile. First, the stability of RNA molecules should be evaluated from the comparison of the rate of formation and the rate of degradation of RNA in open systems. Our prebiotic reaction models of phosphodiester bond formation suggest that at high temperatures the accumulation of RNA may be possible. However, an RNA world entirely consisting of RNA molecules is unlikely to occur because the biologically important interactions are not effective for the bare RNA molecules at high temperatures. Second, since enzymes presently mediate most biological reactions, evaluation of the accumulation of RNA should be based on the comparison between the enzymatic and non-enzymatic reaction rates. Hence, the evaluation of the primitive enzymatic reaction rates at high temperatures has been attempted. There is a large difference between the present enzymatic reaction rates at 25–90 °C and the non-enzymatic reaction rates at high temperatures of 200–300 °C. It is thus possible that prebiotic enzyme-like assemblies could have facilitated the accumulation of RNA molecules at hydrothermal vent temperatures.