Selective catalytic reduction with NH 3 (NH 3 −SCR) is the most efficient technology to reduce the emission of nitrogen oxides (NO x ) from coal-fired industries, diesel engines, etc. Although V 2 O 5 −WO 3 (MoO 3 )/TiO 2 and CHA structured zeolite catalysts have been utilized in commercial applications, the increasing requirements for broad working temperature window, strong SO 2 /alkali/heavy metal-resistance, and high hydrothermal stability have stimulated the development of new-type NH 3 −SCR catalysts. This review summarizes the latest SCR reaction mechanisms and emerging poisonresistant mechanisms in the beginning and subsequently gives a comprehensive overview of newly developed SCR catalysts, including metal oxide catalysts ranging from VO x , MnO x , CeO 2 , and Fe 2 O 3 to CuO based catalysts; acidic compound catalysts containing vanadate, phosphate and sulfate catalysts; ion exchanged zeolite catalysts such as Fe, Cu, Mn, etc. exchanged zeolite catalysts; monolith catalysts including extruded, washcoated, and metal-mesh/foam-based monolith catalysts. The challenges and opportunities for each type of catalysts are proposed while the effective strategies are summarized for enhancing the acidity/redox circle and poison-resistance through modification, creating novel nanostructures, exposing specific crystalline planes, constructing protective/sacrificial sites, etc. Some suggestions are given about future research directions that efforts should be made in. Hopefully, this review can bridge the gap between newly developed catalysts and practical requirements to realize their commercial applications in the near future.

The excited states of the three retinal proteins, bovine rhodopsin (Rh), bacteriorhodopsin (bR), and sensory rhodopsin II (sRII) were studied using the symmetry-adapted cluster-configuration interaction (SAC-CI) and combined quantum mechanical and molecular mechanical (QM/MM) methods. The computed absorption energies are in good agreement with the experimental ones for all three proteins. The spectral tuning mechanism was analyzed in terms of three contributions:  molecular structures of the chromophore in the binding pockets, electrostatic (ES) interaction of the chromophore with the surrounding protein environment, and quantum-mechanical effect between the chromophore and the counterion group. This analysis provided an insight into the mechanism of the large blue-shifts in the absorption peak position of Rh and sRII from that of bR. Protein ES effect is primarily important both in Rh and in sRII, and the structure effect is secondary important in Rh. The quantum-mechanical interaction between the chromophore and the counterion is very important for quantitative reproduction of the excitation energy. These results indicate that the present approach is useful for studying the absorption spectra and the mechanism of the color tuning in the retinal proteins.

The yellow-green luminescence from firefly luciferase has long been understood to be the emission from enol-oxyluciferin. However, a recent experiment showed that an oxyluciferin constrained to the keto form produced a yellow-green emission in luciferase (Branchini, B. R.; Murtiashaw, M. H.; Magyar, R. A.; Portier, N. C.; Ruggiero, M. C.; Stroh, J. G. J. Am. Chem. Soc. 2002, 124, 2112-2113). The present quantum mechanical/molecular mechanical and symmetry-adapted cluster-configuration interaction (SAC-CI) theoretical study supports the keto-form to be the yellow-green bioluminescence state in luciferase. We give the theoretically optimized structure of the excited state of oxyluciferin within luciferase, which gives luminescence calculated by the SAC-CI method that is close to the experimental value. Coulombic interactions with neighboring residues, in particular Arg218 and the phosphate group of AMP, play important roles in the color-tuning mechanism. Transformation to the enol form is energetically unfavorable in the luciferase environment. The twisted intramolecular charge-transfer (TICT) state is meta stable and would be easily relaxed to the co-planer structure. Further analyses were performed to verify the spectral-tuning mechanism based on the protonation state and the resonance structure of oxyluciferin.