Search

Nitrogen oxides released from the combustion of fossil fuels are one of the main air pollutants. Selective catalytic reduction technology is the most widely used nitrogen oxide removal technology in the industry. With the development of nanomaterials science, more and more novel nanomaterials are being used as catalysts for the selective reduction of nitrogen oxides. In recent years, metal-organic frameworks (MOFs), with large specific surface areas and abundant acid and metal sites, have been extensively studied in the selective catalytic reduction of nitrogen oxides. This review summarizes recent progress in monometallic MOFs, bimetallic MOFs, and MOF-derived catalysts for the selective catalytic reduction of nitrogen oxides and compares the reaction mechanisms of different catalysts. This article also suggests the advantages and disadvantages of MOF-based catalysts compared with traditional catalysts and points out promising research directions in this field. [ABSTRACT FROM AUTHOR]

With the on‐going development of nanotechnology, iron‐containing nanomaterials have received much attention in wastewater treatment and site remediation. Here, we synthesized a biochar‐supported iron oxide nanocomposite (FemOn/BC) by simply pyrolysing rice root, which is a natural source both of iron and carbon. The FemOn/BC nanocomposite nicely preserved the vascular bundle structure of rice root. With iron oxide doped on the mesoporous biocarbon, the composite has the usability as a Fenton‐like catalyst in the Fenton system. FemOn/BC‐700 (pyrolysis at 700 °C) was selected to catalysis the reactive brilliant red X‐3B degradation. Under the same catalytic effect, the service life of FemOn/BC‐700 almost doubles that of iron microparticles. We believe this green and energy‐efficient method might have value in biomass usage and helps sustainable development. [ABSTRACT FROM AUTHOR]

Boron-doped carbon nanodot materials, comprising evenly distributed BC3-nanodots in a layered carbon matrix, are prepared through a pre-assembly assisted carbonization synthetic strategy. The prepared materials are endowed with high electron affinity and distortion resistance, which provides a stable framework while generating affinity to substrates. [ABSTRACT FROM AUTHOR]

• CSWO of M−NA and nitrogen conversion by CuCo 2 O 4 catalyst was investigated. • Degradation pathways and nitrogen migration mechanism of M−NA were proposed. • Elevate temperature can promote NO 3 – to NO 2 –, resulting in NH 4 + with NO 2 – to form N 2. • CuCo 2 O 4 catalyzing the reaction of ·NO 2 with ·NH 4 , hastening N 2 generation. • CuCo 2 O 4 may induce a reaction between the nitro and amino groups on M−NA to form N 2. Catalytic subcritical water oxidation (CSWO) of M−nitroaniline (M−NA) was investigated in a fused quartz tube reactor (FQTR) to determine the effects of reaction parameters on M−NA mineralization rate, total nitrogen (TN) removal rate and nitrogen-containing products distribution. The results indicated that the TN removal rate was only 26.36 % at 200 °C, 200 % excess oxidant and 15 min residence time, while the TN removal rate reached 67.83 % at 360 °C in SWO of M−NA. Compared with SWO of M−NA, the mineralization rate and TN removal rate of CSWO of M−NA increased by about 10 % and 17.83 %, respectively. The main reason is mainly attributed to CuCo 2 O 4 catalyzing the preferential reaction of ·NO 2 with ·NH 4 , hastening N 2 generation. Alternatively, the CuCo 2 O 4 catalyst may induce a direct reaction between the nitro and amino groups on M−NA within the benzene ring to form N 2. Moreover, degradation pathways and nitrogen migration mechanism of M−NA under SWO/CSWO conditions were proposed. These crucial findings are expected to guide the development of environmentally sustainable catalytic technologies towards addressing significant water pollution challenges. [ABSTRACT FROM AUTHOR]

[Display omitted] • Inactive Au/TiO 2 can be activated by Cl radicals. • Once Cl is consumed, the reaction will be terminated, although a large amount of supported cationic Au remains. • The Au(I)–Au(III) redox couple is responsible for triggering the reaction. Supported cationic gold (Au) has been recognized as an active site of acetylene hydrochlorination for decades; however, it remains ambiguous why its loading on carbon-based materials is active but that on metal oxides (e.g., titania, TiO 2) is virtually inactive. For the inactive Au/TiO 2 catalyst, the Au(I)–Au(III) redox couple cannot be constructed in the presence of oxidizing gas (NO, N 2 O, and NO 2), which is thermally desorbed from the catalyst synthesis when aqua regia is used. Surprisingly, the inactive Au/TiO 2 can be activated when it is impregnated with trichloromethane, CHCl 3 , which releases the radical (Cl) to trigger the Au(I)–Au(III) redox couple. Once Cl radicals are consumed, the reaction will be terminated, although a large amount of supported cationic Au remains. The terminated Au/TiO 2 catalyst can be reactivated by adding Cl again. In contrast to the carbon-supported cationic Au system, the inability to build Au(I)–Au(III) redox couples is the dominant reason for the inactivity of metal-oxide-supported Au catalysts and provides a new perspective on activating metal-oxide-supported metal-based hydrochlorination catalysts. [ABSTRACT FROM AUTHOR]

• Catalytic oxidation of o -ClA and nitrogen transformation in HCW were investigated. • A flexible micro-reactor platform consist of FQTR and Raman spectroscopy was developed. • Mn 2 O 3 improved the degradtion of ammonia-N and inhibited the production of nitrate-N. • o -Chlorophenol was the main intermediate product of o -ClA in HCWO process. • The potential degradation pathway of o -ClA was proposed. Catalytic oxidation of o -chloroaniline (o- ClA) in hot compressed water (HCW) was investigated in a fused quartz tube reactor (FQTR) to determine the effects of catalyst, temperature, oxygen stoichiometric ratio (OSR) and reaction time on o- ClA mineralization, total nitrogen (TN) removal rate and nitrogen-containing products distribution. The results showed that o -ClA can be effectively degraded in HCW. With the increased of OSR, retention time and temperature or added of Mn 2 O 3 as catalyst, the mineralization rate of o -ClA and the removal rate of TN increased. Ammonia-N was the main nitrogen-containing intermediate product of o -ClA degradation, however, when the oxidant was excessive, ammonia-N was oxidized to form nitrate-N. Althought the catalytic effect of Mn 2 O 3 on the mineralization of o -ClA was not outstanding, it promoted the removal of ammonia-N from the benzene ring, improved the degradtion of ammonia-N, and inhibited the production of nitrate-N. GC–MS analyzed results indicated that o -chlorophenol was the main degradation intermediate product of o -ClA in HCWO process. Meanwhile, the potential degradation pathway of o -ClA was proposed. This work thus provides basic knowledge about o -ClA catalytic oxidation removal in HCW process. [ABSTRACT FROM AUTHOR]

• Palladium-based catalysts with distinct nanostructures are successfully synthesized. • Pd SAC exhibits excellent activity and stability for acetylene hydrochlorination. • Pyridinic nitrogen is responsible for stabilizing palladium species. • Reaction mechanism is affected by pyridinic nitrogen. Alternative palladium (Pd)-based catalysts to toxic mercuric chloride catalysts in vinyl chloride manufacture via acetylene hydrochlorination is currently limited by the lack of efficient and durable active sites. Here, the catalytic behavior of Pd-based catalysts with tunable nanostructures and coordination bonds were investigated. The evolution of Pd entities were precisely regulated by controlled thermal treatment. Pyridinic nitrogen is shown to regulate the nanostructures and coordination bonds of Pd sites, improve the thermal stability of Pd atoms, promote the adsorption of acetylene and enrich hydrogen chloride. These results indicate that Pd single-atom is more active than Pd nanoparticle or Pd cluster. The catalytic performance of Pd single-atom catalyst can be further improved by substituting Pd-Cl bond with Pd-N bond, with PdN 2 identified as the efficient and durable active sites. Furthermore, the enrichment of hydrogen chloride enables the Pd single-atom catalysts to produce vinyl chloride via a non-hydrogen chloride excess method, which is a breakthrough in the existing industrial system. Our strategy for controlling the catalytic behavior of Pd sites is of a broad application prospect for the precise control and design of metal active sites. [ABSTRACT FROM AUTHOR]