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Synthesis of an aromatic N-heterocycle derived from biomass and its use as a polymer feedstock
No full textAromatic N-heterocyclic compounds are very important chemicals, which are currently produced mostly from petroleum. Here we report that a pyridazine-based compound 6-(4-hydroxy-3-methoxyphenyl) pyridazin-3(2H)-one (GSPZ) can be efficiently synthesized by the Friedel-Crafts reaction of guaiacol and succinic anhydride, both of which can be derived from biomass. GSPZ is then treated with bio-based epichlorohydrin to prepare the epoxy resin precursor GSPZ-EP. With 4,4'-diaminodiphenylmethane as curing agent, GSPZ-EP possesses higher glass transition temperature (187 degrees C vs. 173 degrees C) and shows a 140%, 70 and 93% increase in char yield (in N-2), storage modulus (30 degrees C) and Young's modulus, respectively when compared with a standard petroleum-based bisphenol A epoxy resin. Moreover, the cured GSPZ-EP shows good intrinsic flame retardancy properties and is very close to the V-0 rating of UL-94 test. This work opens the door for production of aromatic N-heterocyclic compounds, which can be derived from biomass and employed to construct high performance polymers
Effects of Ni particle size on amination of monoethanolamine over Ni-Re/SiO2 catalysts
No full textNi-Re/SiO2 catalysts with controllable Ni particle sizes (4.5-18.0 nm) were synthesized to investigate the effects of the particle size on the amination of monoethanolamine (MEA). The catalysts were characterized by various techniques and evaluated for the amination reaction in a trickle bed reactor at 170 degrees C, 8.0 MPa, and 0.5 h(-1) liquid hourly space velocity of MEA (LHSVMEA) in NH3/H-2 atmosphere. The Ni-Re/SiO2 catalyst with the lowest Ni particle size (4.5 nm) exhibited the highest yield (66.4%) of the desired amines (ethylenediamine (EDA) and piperazine (PIP)). The results of the analysis show that the turnover frequency of MEA increased slightly (from 193 to 253 h(-1)) as the Ni particle sizes of the Ni-Re/SiO2 catalysts increased from 4.5 to 18.0 nm. Moreover, the product distribution could be adjusted by varying the Ni particle size. The ratio of primary to secondary amines increased from 1.0 to 2.0 upon increasing the Ni particle size from 4.5 to 18.0 nm. Further analyses reveal that the Ni particle size influenced the electronic properties of surface Ni, which in turn affected the adsorption of MEA and the reaction pathway of MEA amination. Compared to those of small Ni particles, large particles possessed a higher proportion of high-coordinated terrace Ni sites and a higher surface electron density, which favored the amination of MEA and NH3 to form EDA. (C) 2019, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved
Transient Bronsted Acid Sites in Propene Aromatization over Zn-Modified HZSM-5 Detected by Operando Dual-Beam FTIR
No full textAn operando dual-beam Fourier transform infrared spectrometer was developed to identify the transient Bronsted acid sites (BAS) in propene aromatization over acidic HZSM-5 and Zn-modified HZSM-5 catalysts under real reaction conditions. The eliminated signals include gas-phase I molecular vibrations and heat irradiation at reaction temperatures. We directly observed that the initial activation of propene over Zn2+ of Zn-modified HZSM-5 generated a substantial number of transient BAS, which serve as active sites for the subsequent aromatization reactions. Moreover, during Transient Bronsted Acid Sites the propene aromatization process, the desorption of aromatic precursors over the Zn2+ of Zn/HZSM-5 is easier than that over the H+ of HZSM-5, resulting in an enhanced aromatics productivity. A density functional theory calculation certified the priority of the metallic Zn2+ sites over BAS in the competitive activation of propene molecules. The generation of transient BAS is energetically favorable
On-line alleviation of poisoning in direct methanol fuel cells with pulse potential strategy
No full textCatalyst poisoning from the impurities in the industrial grade methanol is a major challenge for the large-scale application of direct methanol fuel cells in low cost. In this work, we systematically investigate the impurities influencing on cell performance, and confirm that the adsorption of carbonyl containing intermediate species derived from the partial electro-oxidation of the impurities is a crucial factor leading to performance degradation. Hence, an on-line alleviation strategy by intermittently applying pulse potential (reduction potential on the anode or oxidation potential on the cathode) is proposed. The applied potential will bring a reductive condition on the anode, which releases the active sites via the reduction of carbonyl containing species adsorbed on platinum-ruthenium electro-catalysts. Based on this strategy, the adsorption of carbonyl containing intermediate species are effectively suppressed, and the decay rate declines by nearly two orders of magnitude than that of a single cell under traditional operation, which paves a way for the practical application of direct methanol fuel cells with industrial grade methanol feed
Rapid On-Site Detection of Illegal Drugs in Complex Matrix by Thermal Desorption Acetone-Assisted Photoionization Miniature Ion Trap Mass Spectrometer
No full textIllegal drug smugglings and crimes have long been a global concern, and an apparatus which can identify drugs on-the-spot is urgently demanded by law enforcement. A thermal desorption acetone-assisted photoionization miniature ion trap mass spectrometer was developed for on-site and rapid identification of illegal drugs at checkpoints. Acetone was chosen for dopant-assisted photoionization, and the sensitivity of selected drugs was further enhanced with protonated analyte molecular ions [M + H](+). For example, the sensitivity of ephedrine was improved by as high as 22-fold. The mass discrimination effect, which was usually considered as a shortcoming of ion trap mass analyzer, was ingeniously utilized to eliminate the protonated acetone reagent ions and maximize the trapping efficiency of analyte ions in mass analyzer. Twenty-seven drugs were analyzed, and the limits of detection (LODs) of selected illegal drugs were at the nanogram level with analysis time of 2 s. Analyte/dopant ion peak intensity ratios in mass spectra could be used for quantitation to improve the quantitative analysis performance of miniature ion trap mass spectrometer equipped with a discontinuous atmospheric pressure interface (DAPI) with the prerequisite that dopant ions and analyte ions could be simultaneously and effectively trapped by the ion trap. The RSD of signal intensity was reduced from 25.3% to 8.5%, and the linear range was extended from 0.5-25 to 0.5-100 ng/mu L for methamphetamine. A temperature-resolved thermal desorption sampling strategy was developed and used to distinguish illegal drug components in plant-based drug samples and drinks containing illegal drugs