To synthesize a high-performance titanium silicalite-1 (TS-1), this paper reports a simple and environmentally friendly approach to regulate the alkalinity in the synthesis of titanium silicalite-1 (TS-1) involving tetrapropylammonium hydroxide (TPAOH) and tetrapropylammonium bromide (TPABr). Essentially, the pH of the synthesis gel was controlled by n(TPAOH/TPA+), while keeping the total tetrapropylammonium cations (TPA+) constant. The study shows that at a relatively moderate alkalinity of pH = 10.7, TS-1 produced exhibits nanocrystalline microstructure favorable for diffusion, contains high contents of TiO4 and TiV, and delivers 94.3% of H2O2 conversion with a turnover frequency of 565.6 mol (mol h)−1 in propylene epoxidation. Through detailed analysis of crystallization processes of TS-1 at different alkalinities, this study unveils the effect of alkalinity on the rate of Si–Ti condensation, which dictates the formation of the framework structure and incorporation of Ti species into the framework. Essentially, only at moderate alkalinity of pH = 10.7, comparable Si–OH and Ti–OH condensation rates permit the highest amount of Ti being inserted in TS-1 as active (TiO4 + TiV) and limits the self-condensation of Ti species to form inactive anatase-TiO2.
Magnéli phase ceramics have gained extensive attention in a variety of fields, including batteries, electrocatalysis , and wastewater treatment, due to their distinctive properties. In this study, high-performance Magnéli phase Ti 4 O 7 ceramics were synthesized by in-situ hot-pressed sintering of titanium (Ti) and titanium dioxide (TiO 2 ) in a single step. The effects of the sintering temperature and Ti content on the phase transformation and morphology of ceramics were investigated. Moreover, the mechanical properties and electrical conductivity of the samples were systematically characterized. Results show that the sample with the Ti/TiO 2 weight ratio of 0.09 sintered at 1000 °C has impressive comprehensive properties, including a high bulk density of 4.281 g·cm −1 , a mean value of flexural strength of 125.58 MPa, and an excellent conductivity of 1129 S·cm −1 . Furthermore, an evolution mechanism of the in-situ sintering for Ti/TiO 2 was discussed based on the experimental data, and the pattern of variation observed by samples can be reasonably explained.
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