Thermal Conversion of Methane to Formaldehyde Promoted by Gold in AuNbO3+ Cluster Cations

In addition to generation of a methyl radical, formation of a formaldehyde molecule was observed in the thermal reaction of methane with AuNbO₃⁺ heteronuclear oxide cluster cations. The clusters were prepared by laser ablation and mass‐selected to react with CH₄ in an ion‐trap reactor under thermal collision conditions. The reaction was studied by mass spectrometry and DFT calculations. The latter indicated that the gold atom promotes formaldehyde formation through transformation of an Au?O bond into an Au?Nb bond during the reaction.     

Methane dehydroaromatization with periodic CH4-H2 switch:A promising process for aromatics and hydrogen

Long-term stability test of Mo/HZSM-5-N catalysts(HZSM-5-N stands for nano-sized HZSM-5) in methane dehydroaromatization(MDA)reaction has been performed with periodic CH4-H2 switch at 1033-1073 K for more than 1000 h.During this test,methane conversion ranges from 13% to 16%,and mean yield to aromatics(i.e.benzene and naphthalene) exceeds 10%.N2-physisorption,XRD,NMR and TPO measurements were performed for the used Mo/HZSM-5 catalysts and coke deposition,and the results revealed that the periodic hydrogenation can effectively suppress coke deposition by removing the inert aromatic-type coke,thus ensuring Mo/HZSM-5 partly maintained its activity even in the presence of large amount of coke deposition.The effect of zeolite particle size on the catalytic activity was also explored,and the results showed that the nano-sized zeolite with low diffusion resistance performed better.It is recognized that the size effect was enhanced by reaction time,and it became more remarkable in a long-term MDA reaction even at a low space velocity.     

Effect of multiple H‐bonding on the properties of polyimides containing the rigid rod groups

To investigate the influence of hydrogen bonding on the properties of polyimides (PIs) containing rigid rod‐like groups, five symmetrical diamines containing benzimidazole, benzoxazole, and hydroxy group were synthesized, and then a series of PIs were prepared. Results showed that hydroxyl‐containing poly(benzoxazole imide)s possess higher glass transition temperature (T_g) and dimensional stabilities than their corresponding poly(benzoxazole imide)s. Moreover, the corresponding poly(benzimidazole imide)s presented the best performances, such as the highest T_g, the highest char yield and the highest dimensional stabilities. The influence of hydrogen bonding of benzimidazole on the properties of PIs was stronger than that of hydroxyl groups. Hydroxyl‐containing poly(benzoxazole imide)s were formed in crosslinking structures after heat treatment at 400 °C. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 570–581     

In-situ SiN combined with etch-stop barrier structure for high-frequency AlGaN/GaN HEMT

The etch-stop structure including the in-situ SiN and AlGaN/GaN barrier is proposed for high frequency applications.The etch-stop process is realized by placing an in-situ SiN layer on the top of the thin AlGaN barrier.F-based etching can be self-terminated after removing SiN,leaving the AlGaN barrier in the gate region.With this in-situ SiN and thin barrier etch-stop structure,the short channel effect can be suppressed,meanwhile achieving highly precisely controlled and low damage etching process.The device shows a maximum drain current of 1022 mA/mm,a peak transconductance of 459 mS/mm,and a maximum oscillation frequency(fmax)of 248 GHz.