•We employ microwave-assisted one step route to fabricate composite molecular sieves.•Template pre-impregnation on SAPO-34 is a key step for attachment by nanosized ZSM-5.•Composite phase together with predominant weak acidity occurs in SAPO-34/ZSM-5.•SAPO-34/ZSM-5 exhibits excellent catalytic performances in MTO reaction at 400 °C.The promising composites comprising of (CHA)SAPO-34 with (MFI)ZSM-5 structures were successfully fabricated by microwave-assisted hydrothermal synthesis and characterized to further investigate their catalytic performance on methanol to olefins (MTO) reaction. The physical mixture, synthesized nanosized ZSM-5 and microsized SAPO-34 were employed as references for exploring the structure-activity correlation. These obtained products were extensively characterized by XRD, SEM, FT-IR, NH3-TPD and N2 adsorption-desorption techniques to investigate their crystalline phase, framework, morphology, acidic sites and pore structure. The SAPO-34/ZSM-5 and ZSM-5/SAPO-34 composites exhibited significantly different frameworks, morphologies, acidic properties, and micro- and mesopores ratios in spite of their similar crystalline phase compositions. The pre-treatment of microscale SAPO-34 impregnated with tetrapropylammonium hydroxide was a determining procedure to obtain well-defined SAPO-34/ZSM-5 composite without phase detachment. The catalytic test results showed that SAPO-34/ZSM-5 composite exhibited excellent catalytic performances with methanol conversion of 98.9% and light olefins selectivity of 91.93% during 60 h continuous reaction at 400 °C as well as induction period of 0.5 h. O2-TPO experimental results showed that low- and high-temperature coke deposition coexisted in SAPO-34/ZSM-5 composite even after 60 h by suppression on diffusion restriction. A synergetic effect of interface phase together with predominant weak acid sites and distinct pore structure is assigned to make essential contributions to enhanced catalytic activity to methanol conversion, superior shape selectivity to light olefins and improved stability for SAPO-34/ZSM-5 composites at mild temperatures of MTO reaction.Download high-res image (448KB)Download full-size image

A series of activated carbons were prepared by H3PO4-mechanical force activation and characterized by N2 adsorption/desorption isotherms, SEM, FTIR, CO/CO2-TPD, and XPS. Adsorption isotherms of CH4 and N2 were measured in the range of 25–760 mmHg at 20 °C and fitted by Langmuir model to calculate separation coefficient of CH4 against N2 (αCH4/N2). Results showed that H3PO4-mechanical force activation had significantly enhanced the micropore volume of activated carbons (ACs), in which the highest micropore volume (0.8 cm3/g) and BET specific area (1966 m2/g) were obtained under the optimum condition of phosphoric acid impregnation ratio of 1:1, activation temperature of 400 °C, and activation time of 60 min. The micropore volume and surface properties of ACs affected its selectivity adsorption ability toward CH4. The ACs with higher micropore volume had a larger adsorption amount of CH4. And the larger the O/C ratio of the ACs was, the larger the oxygen-containing groups on the ACs would be, which can improve the surface polarity of ACs and enhance the adsorption ability of N2 with certain polarity, and thus make the ACs having the smaller separation factor of αCH4/N2. Among all of the samples, AC-1-400 with the largest micropore volume and O/C ratio had the highest CH4 adsorption amount but the smallest αCH4/N2.

Carbide slag was used as the calcareous materials for the first time to prepare xonotlite via dynamic hydrothermal synthesis. The effects of influential factors including different calcination temperatures, pretreatment methods of the carbide slag and process parameters of hydrothermal synthesis on the microstructure and morphology of xonotlite were explored using XRD and SEM techniques. The results indicate that the carbide slag after proper calcination could be used to prepare pure xonotlite; and different calcination temperatures have little effect on the crystallinity of synthesized xonotlite, but have great impact on the morphology of secondary particles. The different pretreatment methods of the carbide slag pose great impact on the crystallinity and morphology of secondary particles of xonotlite. Xonotlite was also synthesized from pure CaO under the same experimental conditions as that prepared from calcined carbide slag for comparison. Little amount of impurities in carbide slag has no effect on the mechanism of hydrothermal synthesizing xonotlite from carbide slag.

The distribution of water channels in the crystal morphology of type-α hemi-hydrated gypsum (α-HH) was theoretically detected to investigate the effect of water channels on the hydration reactivity of hemi-hydrate phosphogypsum (HPG). Results showed that water channels were mainly distributed in the cylinders of α-HH crystal, whereas no water channel existed in the conical surfaces parallel to the z-axis. Increasing the number of water channels was critical to enhance the hydration activity of HPG compared with the hydration reactivity of industrial HPG and type-α high-strength gypsum. Controlling the technological parameters of crystallization by concentration of liquid-phase SO42 − made it possible to obtain HPG which had the stumpy crystals of α-HH and high hydration reactivity.The mixed solution (36 wt% P2O5 and 20 mg·ml− 1 SO42 −) was prepared with phosphoric acid and sulfuric acid, and then heated to 95 °C. Apatite powders were slowly and evenly added into the mixed solution, and stirred at a speed of 135 r·min− 1. A certain mass of sulfuric acid was again poured into the reaction tank at a dropping speed of 4.5 g·min− 1. After 150 min of allowing crystals to grow, the slurry was filtered to obtain hemi-hydrate phosphogypsum having the stumpy crystals of type-α hemi-hydrated gypsum and high hydration reactivity.Download full-size image