Adsorptive and catalytic properties in the removal of volatile organic compounds over zeolite-based materials

Volatile organic compounds（VOCs） are a major component in air pollutants and pose great risks to both human health and environmental protection. Currently, VOC abatement in industrial applications is through the use of activated carbons as adsorbents and oxide-supported metals as catalysts. Notably, activated carbons easily adsorb water, which strongly hinders the adsorption of VOCs; conventional oxides typically possess relatively low surface areas and random pores, which effectively influence the catalytic conversion of VOCs. Zeolites, in contrast with activated carbons and oxides, can be designed to have very uniform and controllable micropores, in addition to tailored wettability properties, which can favor the selective adsorption of VOCs. In particular, zeolites with selective adsorptive properties when combined with catalytically active metals result in zeolite-supported metals exhibiting significantly improved performance in the catalytic combustion of VOCs compared with conventional oxide-supported catalysts. In this review, recent developments on VOC abatement by adsorptive and catalytic techniques over zeolite-based materials have been briefly summarized.

Transition metal-nitrogen sites for electrochemical carbon dioxide reduction reaction

Electrochemical CO2 reduction reaction(CO2RR)powered by renewable electricity has emerged as the most promising technique for CO2 conversion,making it possible to realize a carbon‐neutral cycle.Highly efficient,robust,and cost‐effective catalysts are highly demanded for the near‐future practical applications of CO2RR.Previous studies on atomically dispersed metal‐nitrogen(M‐Nx)sites constituted of earth abundant elements with maximum atom‐utilization efficiency have demonstrated their performance towards CO2RR.This review summarizes recent advances on a variety of M‐Nx sites‐containing transition metal‐centered macrocyclic complexes,metal organic frameworks,and M‐Nx‐doped carbon materials for efficient CO2RR,including both experimental and theoretical studies.The roles of metal centers,coordinated ligands,and conductive supports on the intrinsic activity and selectivity,together with the importance of reaction conditions for improved performance are discussed.The mechanisms of CO2RR over these M‐Nx‐containing materials are presented to provide useful guidance for the rational design of efficient catalysts towards CO2RR.

Organic‐free synthesis of MOR nanoassemblies with excellent DME carbonylation performance

Seed‐assisted low alkalinity gel system was developed to explore the organic‐free synthesis of MORzeolite.MOR nanoassemblies with Si/Al ratio(SAR)up to 9.4 and high solid yield(84–94%)weresuccessfully obtained under controlled low alkalinity conditions.Characterization results demonstratethat the acid strength increases in parallel with the SAR,while the total acid amount and theproton distribution in the main channels and the side pockets are similar for the samples.The protondistribution in the H‐MOR is not straightforwardly related to the Na+distribution in theas‐synthesized MOR,implying the transfer of the protons among the oxygen sites of framework Tatom.Relative to low‐silica samples I‐5.3 and I‐7.4,sample I‐9.4 displays the best mass transferperformance and accessibility of the acid sites by pyridine due to its relatively low Al density andmild dealumination degree.Correspondingly,sample I‐9.4(pyridine‐modified catalyst)shows thebest activity with ca.100%selectivity of methyl acetate(MAc)in the DME carbonylation reaction.The high steady MAc yield(6.8 mmol/g/h)over sample I‐9.4 suggests the promising application ofMOR nanoassemblies synthesized by this economical organic‐free strategy.

Hydrothermal synthesis and catalytic performance of bulky titanium silicalite-1 aggregates assembled by bridged organosilane

A facile and effective method to synthesize TS‐1zeolite aggregates has been presented.The crystallization of silanized seeds and nanocrystallites led to large and irregular TS‐1zeolite aggregates ranging from5to40μm in size,based on the special sol‐gel chemistry of bridged organosilane.Epoxidation of1‐hexene and cyclohexene was used as a probe reaction to investigate the catalytic performance of the resulting materials.These TS‐1zeolite aggregates possessed both the conventional nanoparticle properties of TS‐1zeolites and variable surface hydrophilic/hydrophobic features,which enhanced the catalytic properties of hydroperoxides for alkene epoxidation.Moreover,the large aggregates effectively simplified the separation procedure during preparation and catalytic reactions.

Studies of Cyclohexane Catalytic Oxidation Processes over Titanium Silicate-1 Zeolite

The catalytic oxidation processes for cyclohexane/H_2O_2/acetone system overthe TS-1 zeolite was studied. Study results have revealed that the cyclohexane conversion was 27%after the reaction proceeded at 100℃ for 2 hours at a cyclohexane/H_2O_2 molar ratio of 0.8. Thecyclohexanol/cyclohexanone molar ratio was 1.3 along with a certain amount of organic acids andesters, the formation of which was closely associated with the oxidation of reaction solvent anddeep oxidation of cyclohexanone and cyclohexanol contained in the reaction products. With respect tothe catalytic oxidation of cyclohexane/H_2O_2 system the selection of appropriate solvent wascritically important.