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Cold-start emissions significantly contribute to total vehicular pollutant emission profiles. There has therefore been a significant amount of research focused on catalytic aftertreatment systems that can mitigate CO, hydrocarbon and NO emissions at low temperatures. Recently, passive NO adsorbers (PNAs) have been developed, and these can store or trap NO at low temperature and are designed to release the trapped NO at higher temperature ranges, where downstream NO reduction catalysts are active. Pd/BEA is reported to be one such PNA. In this study its NO storage at low temperatures and release at higher temperatures was characterized using temperature programmed (TP) experiments and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The influence of CO was investigated and was shown to improve the amount stored at low temperature and also induce higher temperature desorption, in a range that is applicable for downstream NO reduction. Without the reductant, NO release primarily occurred at temperatures too low to be practically relevant. Graphical Abstract: [ABSTRACT FROM AUTHOR]

An effective and rapid procedure to synthesize hierarchical MOR (Hi-MOR) nanosheets by self-assembly between subnanocrystals and organic templates was reported. The hierarchical pore systems provided a large quantity of Brønsted acid sites. Compared with conventional mordenite, Hi-MOR showed higher activity, xylene selectivity and longer catalytic life in the reaction of toluene disproportionation, thanks to its excellent diffusion from hierarchical structure. Graphical Abstract: Hierarchical morednite (Hi-MOR) nanosheets were synthesized by self-assembly between subnanocrystals and organic templates.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Hierarchical zeolites with improved diffusion rate are considered the best strategy to eliminate the limitation of purely microporous network in typical zeolite materials. Herein, hierarchical MFI (Hi-MFI) and hierarchical MOR (Hi-MOR) zeolites with controlled morphology were directly synthesized over modulating grow kinetics. The synthetic parameters were investigated systematically, including gel aging and crystallizing conditions. Using hexadecyl trimethyl ammonium bromide (CTAB) and tetrapropyl ammonium bromide (TPABr) as templates, Hi-MFI nanosheets and sphere-like zeolites were obtained. Besides, unilamellar, multilamellar, nanorod and worm-like Hi-MOR zeolites were synthesized in the presence of CTAB and polyethylene glycol (PEG). The transalkylation of toluene and 1,3,5-trimethylbenzene to xylene performance showed that the hierarchical structure of MFI and MOR zeolites enable zeolite with improved 1,3,5-trimethylbenzene conversion and xylene selectivityGraphical Abstract: Controlled synthesis of hierarchical MFI and MOR zeolites over modulating the grow kinetics. [ABSTRACT FROM AUTHOR]

The porous alumina catalysts with different acidity were prepared and tested for dehydrofluorination of 1,1,1,2-tetrafluoroethane to synthesize trifluoroethylene. The XRD, BET, SEM, NH-TPD and py-IR techniques were used to characterize the alumina catalysts with different calcination temperatures. The porous θ-AlO showed the excellent catalytic performance, with 35.1 % conversion and the selectivity to trifluoroethylene of 99.0 %. The active sites of catalysts for formation of trifluoroethylene are appropriate weak Lewis acid sites, and the strong Lewis acid sites may result in its rapid deactivation, due to the coke or polymerization of trifluoroethylene. Graphical Abstract: Dehydrofluorination of 1,1,1,2-tetrafluoroethane (CFCFH) is a promising route to synthesize trifluoroethylene over θ-AlO, the conversion is 35.1 % and the selectivity to trifluoroethylene is 99 % at 450 °C. It was suggested that appropriate number of weak Lewis acid sites was beneficial to the catalysis for dehydrofluorination of CFCFH, the weak Lewis acid sites as the active sites of synthesis of trifluoroethylene. On the other hand, the strong Lewis acid sites easily result in deactivation of catalysts derived from the coke or polymerization of trifluoroethylene.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

In this study we examine the NO/NO-NH-SCR system over Cu-BEA with varying Cu loading. Significantly higher selective catalytic reduction (SCR) activity is observed at low temperature on highly loaded copper samples, whereas the reverse trend is noticed at high temperature. The NO formation is substantially increased over 'over-exchanged' Cu sites, where Cu co-ordinate to one Al and charge-balanced with one OH-group. This is also the case for NO reaction with NH to produce NO. Using transient experiments the formation/decomposition of ammonium nitrate species are examined. The decomposition depends on the temperature, the sequence of the feed as well as the type of copper species present. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]