Catalytic Performance of Activated Carbon Supported Tungsten Carbide for Hydrazine Decomposition

Accessing the position-specific 18O/16O ratios of lignin monomeric units from higher plants with highly selective hydrogenolysis followed by GC/Py/IRMS analysis

The ¹⁸O/¹⁶O of lignin at bulk, molecular and positional levels can be used to extract valuable information about climate, plant growth environment, plant physiology, and plant metabolism. Access to the individual oxygen isotope compositions (δ¹⁸O) in the lignin monomeric units is, however, challenging as depolymerization of lignin to release the monomeric units may cause isotope fractionation. We have developed a novel method to measure the δ¹⁸O of the three oxygens (O-3, O-4 and O-5) attached to the aromatic ring of the monomeric units (bearing no oxygen in their side chains) releasable by highly selective W₂C/AC (tungsten carbide supported by activated carbon)-catalyzed hydrogenolysis of lignin. O-4 is obtained by measuring the δ¹⁸O of H-type monomeric unit, while O-3 and O-5 can be calculated following isotope mass balance between H, G and S-type monomeric units measurable simultaneously with GC/Py/IRMS (gas chromatography-pyrolysis-isotope ratio mass spectrometry). The measurement precisions are better than 1.15 mUr and 4.15 mUr at molecular and positional levels, respectively. It was shown that there were a δ¹⁸O_H > δ¹⁸O_G > δ¹⁸O_S isotopic order in the herbaceous plant lignin and an (inclusive) opposite order in woody plant lignin. Such differences in isotopic order is likely to be caused by the fact that both L-tyrosine, which carries an ¹⁸O-enriched leaf water signal, and L-phenylalanine, which carries mainly a molecular O₂ isotopic signal, serve as the precursors for lignin biosynthesis in herbaceous plants while only the latter serves as precursor for lignin biosynthesis in woody plants. We have highlighted the potential application of such molecular and positional levels isotopic signals in plant physiological, metabolic, lignin biosynthetic and climate studies.

The Deoxygenation of Jatropha Oil to High Quality Fuel via the Synergistic Catalytic Effect of Ni, W2C and WC Species

Tungsten carbide-based materials have good deoxygenation activity in the conversion of biomass. In this paper, catalysts with different nickel–tungsten carbide species were prepared by tuning the reduction temperature and Ni loading, and the effects of these different tungsten carbide species in the conversion of jatropha oil were studied. XRD, XPS, TEM, HRTEM, Raman, H2-TPR, ICP-AES were used to characterize the catalysts. The results suggested that metallic W was gradually carburized to W2C species, and W2C species was further carburized to WC species with the increase in reduction temperature and Ni loading. The obtained 10Ni10W/AC-700 catalyst exhibited outstanding catalytic performance with 99.7% deoxygenation rate and 94.5% C15-18 selectivity, which were attributed to the smallest particle size, the best dispersion, the most exposed active sites, and the synergistic effect of Ni, W2C and WC species.

A Computational Study of the Heterogeneous Synthesis of Hydrazine on Co3Mo3N

Abstract

Periodic and molecular density functional theory calculations have been applied to elucidate the associative mechanism for hydrazine and ammonia synthesis in the gas phase and hydrazine formation on Co₃Mo₃N. We find that there are two activation barriers for the associative gas phase mechanism with barriers of 730 and 658 kJ/mol, corresponding to a hydrogenation step from N₂ to NNH₂ and H₂NNH₂ to H₃NNH₃, respectively. The second step of the mechanism is barrierless and an important intermediate, NNH₂, can also readily form on Co₃Mo₃N surfaces via the Eley–Rideal chemisorption of H₂ on a pre-adsorbed N₂ at nitrogen vacancies. Based on this intermediate a new heterogeneous mechanism for hydrazine synthesis is studied. The highest relative barrier for this heterogeneous catalysed process is 213 kJ/mol for Co₃Mo₃N containing nitrogen vacancies, clearly pointing towards a low-energy process for the synthesis of hydrazine via a heterogeneous catalysis route.

Graphical Abstract

Electronic supplementary material

The online version of this article (doi:10.1007/s10562-017-2080-y) contains supplementary material, which is available to authorized users.

Ring opening of decalin over bifunctional Ni–W carbide/Al2O3–USY catalysts and monofunctional acid Ni–W oxide/Al2O3–USY

The ring opening reaction of decalin was studied over two types of catalyst, including bifunctional catalysts (Ni–W carbide/Al₂O₃–USY) and monofunctional acid catalysts (Ni–W oxide/Al₂O₃–USY) with different amounts of metal loading.

Evaluating and optimizing pretreatment technique for catalytic hydrogenolysis conversion of corn stalk into polyol

A combinative pretreatment technology of steam explosion (SE) and alkali was applied to enhance hydrogenolysis conversion of corn stalk into polyol with Ni-W2C or Fe-Mn-K catalyst. The results showed that treatments corn stalk with 0.4 MPa SE and alkali removed 84.16 wt% of hemicellulose and 71.83 wt% of lignin and thereby increased the cellulose content from 31.54 to 80.41 wt%. But the glucose loss was insignificant during pretreatment. Data from catalytic hydrogenolysis showed that pretreatment corn stalk with 0.4 MPa SE and alkali improved the yield of polyol, and about 20.38 wt% of ethylene glycol and 52.36 wt% of glycerol were produced after catalysis with Ni-W2C/(coconut shell activated carbon, CSAC). Based on the yield of polyol, the catalytic performance of Ni-W2C/CSAC was significantly better than those of Ni-W2C/(coal-based activated carbon) and Fe-Mn-K/(amorphous carbon).

Nickel-promoted tungsten carbide catalysts for cellulose conversion: effect of preparation methods

A series of Ni-promoted W(2) C catalysts was prepared by means of a post-impregnation method and evaluated for the catalytic conversion of cellulose into ethylene glycol (EG). Quite different from our previously reported Ni-W(2) C/AC catalysts, which were prepared by using the co-impregnation method, the introduction of Ni by the post-impregnation method did not cause catalyst sintering, but resulted in redispersion of the W component, which was identified and characterized by means of XRD, TEM, and CO chemisorption. The highly dispersed Ni-promoted W(2) C catalyst was very active and selective in cellulose conversion into EG, with a 100% conversion of cellulose and a 73.0% yield in EG. The underlying reason for the enhanced catalytic performance was most probably the significantly higher dispersion of active sites on the catalyst.