Yongxiang Zhao

Amorphous aluminosilicates used as acid catalysts for tetrahydrofuran polymerization

Al-MCM-41, Al-SBA-15 and silica-alumina composite oxides (HAS) were compared as catalysts in tetrahydrofuran polymerization. These catalysts were characterized by N2 physisorption, scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction and temperature-programmed desorption of ammonia (NH3-TPD). The catalytic test results showed that both weak and medium acid sites were active for THF polymerization. The catalysts with higher total acidity and larger pore size showed higher catalytic activity. The coexistence of mesopores and macropores in HAS(7.5) which has Si/Al ratio of 7.5 highly improved the catalytic activity and prolonged the catalyst life comparing with the mesoporous Al-MCM-41, Al-SBA-15. This is probably ascribed to that the reactive places are mainly offered by mesopores and at the same time the enhanced diffusion and mass transfer process is introduced by macropores. The number-average molecular weight (Mn) depended on the size of mesopores due to the shape selectivity.

Adsorption Kinetics and Interfacial Dilational Properties of Fluorinated Hyperbranched Polymer at n-Decane/Water Interface

The dynamic interfacial tension of a series of novel hyperbranched fluoropolymer with different hydrophobic chain lengths at the n-decane/water interface is examined. The kinetics of adsorption of the polymers is analyzed with pure diffusion model and diffusion-reorientation model. The results show that at the earlier stages of adsorption, the transport of the fluoropolymer from the n-decane solution to the interface is governed by pure diffusion-controlled mechanism; at the end stages of adsorption, the mixed diffusion-reorientation mechanism is more reasonable in describing the adsorption kinetics. Moreover, the influences of oscillating frequency and bulk concentration on dilational properties are explored. The results show that the hydrophobic chain length of the polymer controls the nature of adsorption film and the film is elastic in nature.

Effect of precipitants on the catalytic performance of Pd–Cu/attapulgite clay catalyst for CO oxidation at room temperature and in humid circumstances

The Pd–Cu/attapulgite clay catalysts were synthesized using a deposition–precipitation method with different precipitants. The as-synthesized catalysts were characterized by ICP-AES, N2-physisorption, XRD, FT-IR, TEM and TPR. Their catalytic activities for CO oxidation were tested by a fixed-bed continuous flow reactor at room temperature and in humid circumstances. The results illustrated that the activity of CO oxidation strongly depended on the precipitant. The best catalytic performance is achieved by using NH3·H2O (PC-AH) or NH4HCO3 (PC-AHC) as precipitants. The crystalline phase of PC-AH and PC-AHC comprised of Cu2Cl(OH)3 and CuO, while the catalysts prepared with NaOH (PC-SH) or NaHCO3 (PC-SHC) as precipitants were mainly CuO. Combined with FT-IR and TEM results, it could be found that Cu2Cl(OH)3 on PC-AH and PC-AHC possessed higher stability than that on PC-SH and PC-SHC due to the different formation process and morphology of Cu2Cl(OH)3 species. The TPR results showed that the Cu2Cl(OH)3 had a strong interaction with Pd species and enhanced reducibility. Moreover, the residual sodium ions on PC-SH and PC-SHC may have adverse effect on the catalytic activity. A suitable precipitant resulted in the most efficient CO oxidation catalyst at room temperature and in humid circumstances.

Geometric design of a Ni@silica nano-capsule catalyst with superb methane dry reforming stability: enhanced confinement effect over the nickel site anchoring inside a capsule shell with an appropriate inner cavity

Catalyst deactivation via severe carbon deposition and metal sintering is a significant obstacle to the industrialization of CO2 reforming of methane (CRM). Previous reports are mainly focused on metal oxide supported catalysts, which were proved to be less effective in eliminating the formation of carbon deposition completely. Here, we report a facile strategy for the preparation of a highly dispersed Ni@SiO2 nano-capsule catalyst, which features a monodisperse capsule and anchored Ni NPs in the inner porous shell. By virtue of this, carbon formation could be sterically hindered due to the sealed space for carbon formation and growth, and therefore excellent catalytic performance was achieved. Through comprehensive characterization and comparison of traditional supported catalysts as well as capsule catalysts with different architectures, the importance of a confined capsule structure in preventing carbon formation was convincingly demonstrated. Our work disclosed a morphological approach that is much more effective in preventing sintering of Ni NPs and suppressing carbon formation simultaneously, therefore shedding new light on the design and preparation of highly stable Ni-based catalysts for reforming reactions.