N2 Transfer Research Articles

Heteronuclear Trimetallic MFe2 and M2 Fe (M=V, Nb, and Ta) Clusters for Dinitrogen Activation.

Catalysts with heteronuclear metal active sites may have high performance in the nitrogen reduction reaction (NRR), and the in-depth understanding of the reaction mechanisms is crucial for the design of related catalysts. In this work, the dissociative adsorption of N2 on heteronuclear trimetallic MFe2 and M2 Fe (M=V, Nb, and Ta) clusters was studied with density functional theory calculations. For each cluster, two reaction paths were studied with N2 initially on M and Fe atoms, respectively. Mayer bond order analysis provides more information on the activation of N-N bonds. M2 Fe is generally more reactive than MFe2 . The coordination mode of N2 on three metal atoms can be end-on: end-on: side-on (EES) for both MFe2 and M2 Fe. In addition, a unique end-on: side-on: side-on (ESS) coordination mode was found for M2 Fe, which leads to a higher degree of N-N bond activation. Nb2 Fe has the highest reactivity towards N2 when both the transfer of N2 and the dissociation of N-N bonds are taken into account, while Ta-containing clusters have a superior ability to activate the N-N bond. These results indicate that it is possible to improve the performance of iron-based catalysts by doping with vanadium group metals.

Facile N≡N Bond Cleavage by Anionic Trimetallic Clusters V3-x Tax C4- (x=0-3): A DFT Study.

Activation of N2 on anionic trimetallic V3-x Tax C4- (x=0-3) clusters was theoretically studied employing density functional theory. For all studied clusters, initial adsorption of N2 (end-on) on one of the metal atoms (denoted as Site 1) is transferred to an of end-on: side-on: side-on coordination on three metal atoms, prior to N2 dissociation. The whole reaction is exothermic and has no global energy barriers, indicating that the dissociation of N2 is facile under mild conditions. The reaction process can be divided into two processes: N2 transfer (TRF) and N-N dissociation (DIS). For V-series clusters, which has a V atom on Site 1, the rate-determining step is DIS, while for Ta-series clusters with a Ta on Site 1, TRF may be the rate-determining step or has energy barriers similar to those of DIS. The overall energy barriers for heteronuclear V2 TaC4- and VTa2 C4- clusters are lower than those for homonuclear V3 C4- and Ta3 C4- , showing that the doping effect is beneficial for the activation and dissociation of N2 . In particular, V-Ta2 C4- has low energy barriers in both TRF and DIS, and it has the highest N2 adsorption energy and a high reaction heat release. Therefore, a trimetallic heteronuclear V-series cluster, V-Ta2 C4- , is suggested to have high reactivity to N2 activation, and may serve as a prototype for designing related catalysts at a molecular level.

Growth, Nitrogen Fixation and Transfer in a Mixed Cropping System of Cowpea-Rice

ABSTRACT Growth, nodulation, nitrogen fixation and transfer of N2 were studied in a mixed cropping system of cowpea (Vigna unguiculata L. (Walp)) and rice (Oryza sativa L.). The treatments consisted of three cropping systems which were: monocrop cowpea, monocrop rice and cowpea/rice mixed cropping. l5N-labelled ammonium sulphate (20 kg N ha−l of atom % l5N excess) was applied evenly in solution to the l5N subplots while the same amount of unlabelled ammonium sulphate was applied in salt form to the l4N subplots. The cropping system, either sole or mixed with rice, did not significantly influence nodule dry weight at any of the sampling dates. Plants of sole cowpea had a higher shoot dry weight than mixed-crop cowpea plants while the growth of rice was essentially the same. Sequential harvests made at 25, 35, 45 and 55 days after planting (DAP) showed that the proportion of nitrogen derived from N2 fixation and the amount of N2 fixed by sole and mixed-crop cowpea were similar. The l5N enrichment data show ...