Stability of Y/MCM-48 composite molecular sieve with mesoporous and microporous structures

AbstractY/MCM-48 composite molecular sieve was hydrothermally synthesized at different crystallization temperatures and crystallization times using ethyl orthosilicate as Si source and cetyltrimethyl ammonium bromide as template with the aid of fluoride ions and was characterized by X-ray diffraction, N2 physical adsorption technique, scanning electron microscopy and transmission electron microscopy. The thermal, hydrothermal, acidic, and basic stabilities of the Y/MCM-48 composite were investigated. The results show that Y/MCM-48 composite molecular sieve with meso- and microporous structures was synthesized successfully at 120°C for 36h. The Y/MCM-48 composite has the surface area of 864m2/g and the average pore size is ca. 2.48nm. The bi-porous structure in composite molecular sieve still maintains its stability even after thermal treatment at 800°C for 4h or hydrothermal treatment at 100°C for 48h. After treatment in 1mol/L hydrochloric acid solution or 1mol/L sodium hydroxide solution for 48h, the Y/MCM-48 composite exhibits good acidic stability. The acidic stability is superior to the basic stability at the same treatment time

ChemInform Abstract: Access to Oxoquinoline Heterocycles by N-Heterocyclic Carbene Catalyzed Ester Activation for Selective Reaction with an Enone.

Organocatalytic ester activation is developed for a highly selective cascade reaction between saturated esters and amino enones. The reaction involves activation of the β-carbon atom of the ester as a key step. This method allows a single-step access to multicyclic oxoquinoline-type heterocycles with high enantiomeric ratios

Fabrication of polylactic acid/hydroxyapatite/graphene oxide composite and their thermal stability, hydrophobic and mechanical properties

A series of polylactic acid/hydroxyapatite/graphene oxide composite (PLA/HA/GO) were fabricated via solution blending and casting method using N,N-dimethyl-formamide (DMF) and CH2Cl2 as mutual solvents. The physicochemical properties of the resulting composites were characterized by means of FT-IR, SEM, TEM, Raman spectra, XRD and N2-physisorption. Particularly, the thermal stabilities, hydrophobic and mechanical properties of PLA/HA/GO composites were systematically investigated. The influences of GO content on thermal stabilities, hydrophobic and mechanical properties of the composites were also evaluated. The results showed that the addition of GO and HA not only improved the thermal stability of PLA, but also improved the hydrophobic property of PLA-based composites. By compared with the PLA/HA/GO composite, the tensile strength of pristine PLA is slight high. The tensile strength and hardness of PLA/HA/GO composites increased with the increase of GO content. The obtained PLA/HA/GO composite may be a promising material for load-bearing orthopedic implants

Investigating the Time-varying Effect of Search Index in Predicting Tourism Volume Using Dynamic Model Averaging

Search index has been gradually used for tourism volume forecasting. While most literature aimed to improve the accuracy of a tourism prediction model, rarely considered the influencing characteristics of the search index in the prediction model. In this study, a dynamic model averaging (DMA) approach is applied to build tourism volume model and to investigate the time-varying effect of search indexes in predicting tourism volume. The tourism volume of Jiuzhai Valley and related search indexes from Baidu Index are considered for experimental purpose. According to the results, search index present time-varying characteristic, specifically, the search indexes of Jiuzhai Valley hotel, Jiuzhai Valley, Jiuzhai Valley map and Jiuzhai Valley guide have higher probabilities in supporting the prediction of tourism volume

Preparation of mesoporous zirconium incorporated MCM-48 solid acid catalyst and its catalytic activity for alkylation of phenol with tert-butyl alcohol

Zirconium incorporated mesoporous MCM-48 solid acid catalysts with the different Si/Zr molar ratios were prepared by modification with H2SO4 and NH4NO3 solution, respectively. Their physicochemical properties were characterized by XRD, TEM, NH3–TPD and N2 physical adsorption. The catalytic performances of these catalysts were investigated by using the alkylation reaction of phenol and tert-butyl alcohol as the target reaction. The results reveal that the SO42−/ZrMCM-48 and H-ZrMCM-48 catalysts still maintained the cubic mesporous structure of MCM-48, but the mesoporous ordering decreased. Under comparable conditions, the catalytic activity of SO42−/ZrMCM-48(25) solid acid catalyst is the highest among all catalysts. The lower reaction temperature is favorable for formation of the 2,4-DTBP and the 4-TBP is easily formed at the higher reaction temperature