Tailoring the microenvironment of Ti sites in Ti-containing materials for synergizing with Au sites to boost propylene epoxidation

Au sites supported on Ti-containing materials(Au/Ti-containing catalyst)are currently considered as a promising catalyst for the propylene epoxidation owing to the synergistic effect that hydrogen peroxide species formed on Au sites diffuses to the Ti sites to form the Ti-hydroperoxo intermedi-ates and contributes to the formation of propylene oxide(PO).In principle,thermal treatment will significantly affect the chemical and physical structures of Ti-containing materials.Consequently,the synergy between tailored Ti sites with different surface properties and Au sites is highly expected to enhance the catalytic performance for the reaction.Herein,we systematically studied the intrinsic effects of different microenvironments around Ti sites on the PO adsorption/desorption and conversion,and then effectively improved the catalytic performance by tailoring the number of surface hydroxyl groups.The Ti^(Ⅵ) material with fewer hydroxyls stimulates a remarkable enhancement in PO selectivity and H_(2) efficiency compared to the Ti^(Ⅵ) material that possessed more hydroxyls,offering a 7-fold and 4-fold increase,respectively.As expected,the Ti^(Ⅵ+Ⅳ) and Ti^(Ⅳ) materials also exhibit a similar phenomenon to the Ti^(Ⅵ) materials through the same thermal treatment,which strongly supports that the Ti sites microenvironment is an important factor in suppressing PO con-version and enhancing catalytic performance.These insights could provide guidance for the rational preparation and optimization of Ti-containing materials synergizing with Au catalysts for propylene epoxidation.

Synthesis of Mesoporous Silica and Ti-containing Molecular Sieves via A Novel Assembly

Thermally stable mesoporous silica and Ti-containing molecular sieves have been synthesized at mild temperature using low-cost and biodegradable --- amphoteric tetradecyl betaine as template. The physicochemical characterizations proved that Ti(IV) could be incorporated in the mesoporous struture.

Understanding Formation Mechanism of Titanate Nanowires through Hydrothermal Treatment of Various Ti-Containing Precursors in Basic Solutions

Titanate nanowires prepared by hydrothermal treatment of Ti02 in NaOH solution have attracted intensive attentions, but the formation mechanism is still under debate. Herein, we report an in-depth study on the formation mechanism through investigating the hydrothermal behavior of various Ti-containing precursors in basic solutions, including Ti, TiN, TiO2, Ti2SnC and Ti2AIN. Based on the results by means of X-ray diffraction （XRD）, transmission electron microscopy （TEM） and Raman spectroscopy, it is demonstrated that the crystal structure of the hydrothermal products is irrespective to the structure of the precursors or the types of basic solution （NaOH or KOH） in use. Alkali ions play an important role in the formation of titanate nanowires. The formation mechanism of the resultant titanate nanowires was proposed to be dissolution-crystallization mechanism.

Hydrothermal conversion of Ti-containing minerals in system of Na_2O–Al_2O_3–SiO_2–CaO–TiO_2–H_2O

Titanium has a great effect on the digestion of bauxite in the Bayer process because it reacts readily at high temperatures in alkaline sodium aluminate solution. Under this consideration, the hydrothermal conversion of Ti-containing minerals in the system of Na2O-Al2O3- SiO2-CaO-TiOz-H2O with increased temperatures was studied based on the thermodynamic analysis and systematic experiments. The results show that anatase converts to AlaTi2SiO12 at low temperatures （60-120℃）, which is similar to anatase in crystal structure. As the temperature continues to rise, Al4Ti2SiO12 decomposes gradually and converts to Ca3TiSi2（Al2Si0.5Ti0.5）O14 at 200 ℃ When the temperature reaches 260℃, CaTiO3 forms as the most stable titanate species for its hexagonal closest packing with O^2- and Ca^2＋. The findings enhance the under-standing of titanate scaling in the Bayer process and clarify the mechanism of how additive lime improves the digestion of diaspore.

Characteristics of Hot Ductility in Steels Containing Nb,Ti

The hot ductility was measured for a series of steels containing Nb and/or Ti with Gleeble-3500 thermo-mechanical simulator.It is found that the effect of austenitizing temperature on hot ductility of Nb-containing steel is significant.As the austenitizing temperature rises up,the shape of embrittling curve (SEC) from V-shape gradually changes to U-shape,and the range of embrittling temperature widens out and the embrittling degree deepens.The SEC of Nb-containing steel is U-shaped and the embrittling temperature range is about 600-1050℃.The initial temperature of embrittlement on the right is nearly independent of carbon content.The SEC of Ti-containing steel is N-shaped and two lowest points are at about 600℃ and the A-F transformation temperature.The SEC of Nb-Ti-containing steel is basically the superposition of two shapes mentioned above.The crack on straightening in continuous casting belongs to intergranular fracture,and the crack on rolling (crack expansion) belongs to transgranular fracture.