No abstract

One-step synthesis of hydrophobic CPs was demonstrated, in which the kinetically-controlled induction period and thermodynamically-based rapid growth process were elucidated.

Nanoprecursors used as a structural promoter (SP) were prepared by a hydrothermal method and named sol-SP.

Three-dimensionally ordered macroporous (3DOM) CoCr2O4 and its supported bimetallic Auy Pt nanocatalysts (xAuyPt/3DOM CoCr2O4, x = 0.49, 0.98, and 1.92 wt%; Au/Pt molar ratio (y) = 0.99, 0.98, and 1.01) were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods, respectively. Physicochemical properties of the samples were characterized by means of various techniques. Catalytic activities of the xAuyPt/3DOM CoCr2O4 samples were evaluated for methane combustion. It is found that the 3DOM CoCr2O4 support possessed a single-phase and cubic spinel-type crystal structure, the xAuyPt/3DOM CoCr2O4 samples displayed a high-quality 3DOM architecture and a surface area of 32-33 m2/g, and the AuyPt nanoparticles (NPs) with a size of 3-5 nm were well dispersed on the 3DOM CoCr2O4 surface. The loading of an appropriate amount of AuyPt NPs could enhance the adsorbed oxygen species concentration and low-temperature reducibility of the sample. Among all of the samples, 0.98Au0.98Pt/3DOM CoCr2O4 showed the best catalytic performance: the T10%, T50%, and T90% (temperatures required for achieving methane conversion of 10, 50, and 90 %, respectively) were 253, 315, and 354 oC at a space velocity of 20,000 mL/(g h). It is concluded that the good activity of 0.98Au0.98Pt/3DOM CoCr2O4 was associated with its highly dispersed Au0.98Pt NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au0.98Pt NPs and 3DOM CoCr2O4.

The clinoptilolites (CPs) with high purity were prepared via structure directing agent (SDA) method combining with hydrothermal method using silica sol as the silica source and aluminum hydroxide as the aluminum source. Their structural features were characterized by X-ray diffraction (XRD) patterns, Fourier transform infrared (FT-IR) spectra, thermal gravimetric (TG) analysis, scanning electron micrograph (SEM) images, 29 Si nuclear magnetic resonance (NMR) profiles. The effects of additive amount and aging time of used SDA, as well as synthetic parameters such as crystallization temperature and crystallization time on their structure and performance were emphasized. Particularly, the activation energies of their crystallization kinetics at different stages of induction period and growth period were calculated on the basis of Arrhenius equation. The results demonstrated that the obtained CPs presented the highest relative crystallinity when the additive amount of used SDA was 1 mL at aging periods of 2 d, otherwise, their relative crystallinity degree was low due to existences of a large number of heterocrystal impurities. Particularly, the apparent activation energy values for induction (E n) and growth (E g) profile were calculated by the Arrhenius equation. The E n value (86.46 kJ/mol) of induction period was much higher than that E g value (9.64 kJ/mol) of growth stage, suggesting that the induction period was the main controlling step during the synthetic CP. Finally, the synthetic CP was employed to preliminarily assess its performances for CH 4 /N 2 separation. These demonstrations provide a promising method for the synthesis of CPs.