Catalyst design strategies towards highly shape-selective HZSM-5 for paraxylene through toluene alkylation

With the shape selective zeolite catalyst,toluene alkylation with methanol to para-xylene(MTPX)technology could produce highly pure para-xylene(PX)in one step.The lower feedstock cost and less energy consumption in products separation make it more competitive compared to the current toluene disproportionation route.Thus,MTPX is regarded as the most reasonable production route for PX production.This article reviews the strategies that applied to the preparation of high-performance catalysts for MTPX,with special focus on the precise control of pore dimension and acid sites distribution in zeolite to achieve the highest selectivity to PX.The outlook of the MTPX catalyst is also proposed to guide the catalyst development in the field.

Crosslinking Kinetics of Polyethylene with Small Amount of Peroxide and Its Influence on the Subsequent Crystallization Behaviors

Crosslinking reactions of high density polyethylene with low peroxide concentrations ranging from 0.1 wt% to 1.0 wt% at temperatures of 170, 180 and 190 ℃ were monitored by rheological measurements. A critical gel forms at the peroxide concentration of 0.2 wt%, where the transition from long chain branching generation to crosslinking network formation could occur. Rheokinetics of crosslinking can be fitted well by Ding-Leonov＇s model. The curing rate k2 at the earlier stage exhibits about 3 times acceleration per 10 ~C with increasing temperature, while the equilibrium modulus G＇ at the fully cured stage is almost independent of temperature. Influences of crosslinking on the subsequent crystallization behaviors were detected by DSC measurements. Above the critical gel concentration, crystallization is largely retarded as evidenced by the lower crystallization temperature Tc and crystallinity Xc due to the network formation. The secondary crystallization valley located at the temperature near 80 ℃ can be observed above the critical concentration, which becomes more evident with the increasing peroxide concentration and curing temperature. This phenomenon provides another evidence of crystallization retardation by the crosslinking network.

Research Trends in Fischer-Tropsch Catalysis for Coal to Liquids Technology

Fischer–Tropsch Synthesis(FTS) constitutes catalytic technology that converts synthesis gas to synthetic liquid fuels and chemicals.While synthesis gas can be obtained from any carbonaceous feedstock,current industrial FTS operations are almost exclusively based on natural gas.Due to the energy structure of China where cheap coal is abundant,coal to liquids(CTL) technology involving coal gasification,FTS and syncrude upgrading is increasingly being considered as a viable option to convert coal to clean transportation fuels.In this brief paper,we review some pertinent issues about Fe-and Co-based FTS catalysts.Fe is better suited to convert synthesis gas derived from coal gasification into fuels.The authors limit themselves to noting some important trends in the research on Fe-based catalysts.They focus on the preparation of phase-pure carbides and innovative cheap synthesis methods for obtaining active and stable catalysts.These approaches should be augmented by(1) computational investigations that are increasingly able to predict not only mechanism,reaction rates and selectivity but also optimum catalyst composition,as well as(2) characterization of the catalytic materials under conditions close to the operation in real reactors.

FDTD analysis of the optical properties of vertical ZnO nanorod array

Based on the structure and dimensions of a vertical ZnO nanorod array(V-ZNA)sample,an ideal 2-D photonic crystal model was established.The optical properties of the V-ZNAs were analyzed with finite-difference time-domain(FDTD)method,and the influences of the geometry parameters,including the circumcircle diameters of the top and bottom surfaces(Dt and Db)and the height(H)of the nanorods,and the pitch between each column(L),were discussed.High transmittance and low reflectance in the waveband of 400–800 nm were proved,and the highest transmittance can be obtained with Dt<50 nm,H=200 nm,and Db/L=0.85,which was verified by Effective Index Method(EIM).The result indicates that V-ZNAs can be used as excellent light coupling element and antireflection material for solar energy applications.