Because of the harsh reaction conditions and relatively low NH3 yield of Haber-Bosch process for synthesized ammonia industry, it is highly desirable to develop an alternative route for more efficient...

Agricultural biomass wastes are an abundant feedstock for biorefineries. However, most of these wastes are not treated in the right way. Here, corn stalks (CSs) were assigned as the raw material to produce cellulose nanofibers (CNFs) via in situ Fenton oxidation treatment. In order to probe the formation mechanism of an in situ Fenton reactor, the bonding interaction of hydrated Fe 2+ ions and fiber has been systemically studied based on adsorption experiments, IR spectroscopy, density functional theory (DFT) calculations, and Raman spectroscopy. The results indicate that the coordination of the hydrated Fe 2+ ion to the fiber generates a quasi-octahedral-coordinated sphere around the Fe center. The Jahn−Teller distortion effect of the Fe center promotes the Fe−O 2 H 2 bonding interaction via reduction of the energy gap of the d z 2 orbital of the Fe center and π 2py /π 2pz orbitals of the H 2 O 2 molecule. The oxidation treatment of the pretreated CS by the in situ Fenton process shows the formation of a new carboxyl group on the fiber surface. The scanning electron microscopy image shows that the Fenton-treated fiber was scattered into the nanosized CNFs with a diameter of up to 50 nm. Both experimental and theoretical studies show that the pseudo-first-order kinetic reaction could describe the in situ Fenton kinetics well. Moreover, the proposed catalytic cycle shows that the large thermodynamic barrier is the cleavage of the O−O bond of H 2 O 2 to generate the • OH radical, and the whole catalytic cycle is found to be spontaneous at room temperature.

Fast selective catalytic reduction of nitrogen oxide with ammonia (NH 3 -SCR) (2NH 3 + NO 2 + NO → 2N 2 + 3H 2 O) has aroused great interest in recent years because it is inherently faster than the standard NH 3 -SCR reaction (4NO + 4NH 3 + O 2 → 4N 2 + 6H 2 O). In the present paper, the mechanism of the fast NH 3 -SCR reaction catalyzed by a series of single-atom catalysts (SACs), M 1 / PTA SACs (PTA = Keggin-type phosphotungstic acid, M = Mn, Fe, Co, Ni, Ru, Rh, Pd, Ir, and Pt), has been systematically studied by means of density functional theory (DFT) calculations. Molecular geometry and electronic structural analysis show that Jahn−Teller distortion effects promote an electron transfer process from N−H bonding orbitals of the NH 3 molecule to the symmetry-allowed d orbitals (d xy and d xd 2 −yd 2 ) of the single metal atom, which effectively weakens the N−H bond of the adsorbed NH 3 molecule. The calculated free energy profiles along the favorable catalytic path show that decomposition of NH 3 to *NH 2 and *H species and decomposition of *NHNOH into N 2 and H 2 O have high free energy barriers in the whole fast NH 3 -SCR path. A good synergistic effect between the Brønsted acid site (surface oxygen atom in the PTA support) and the Lewis acid site (single metal atom) effectively enhances the decomposition of NH 3 to *NH 2 and *H species. M 1 /PTA SACs (M = Ru, Rh, Pd, and Pt)were found to have potential for fast NH 3 -SCR reaction because of the relatively small free energy barrier and strong thermodynamic driving forces. We hope our computational results could provide some new ideas for designing and fabricating fast NH 3 -SCR catalysts with high activity.

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