Selective catalytic reduction of NOx with NH3 on Mn, Co-BTC-derived catalysts: Influence of thermal treatment temperature

Performance and Mechanism of Co and Mn Loaded on Fe-Metal-Organic Framework Catalysts with Different Morphologies for Simultaneous Degradation of Acetone and NO by Photothermal Coupling

VOCs can be used instead of ammonia as a reducing agent to remove NO, achieving the effect of removing VOCs and NO simultaneously. Due to the high energy consumption and low photocatalytic efficiency required for conventional thermocatalytic purification, photothermal coupled catalytic purification can integrate the advantages of photocatalysis and thermocatalysis in order to achieve the effect of pollutants being treated efficiently with a low energy consumption. In this study, samples loaded with Co and Mn catalysts were prepared using the hydrothermal method on Fe-MOF with various morphologies. The catalytic performance of each catalyst was analyzed by studying the effects of their physicochemical properties through various characterizations, including XRD, SEM, BET, XPS, H2-TPR, TEM and O2-TPD. The characterization results demonstrated that the specific surface area, pore volume, high valence Co and Mn atoms, surface adsorbed oxygen and the abundance of oxygen lattice defects in the catalysts were the most critical factors affecting the performance of the catalysts. Based on the results of the performance tests, the catalysts prepared with an octahedral-shaped Fe-MOF loaded with Co and Mn showed a better performance than those loaded with Co and Mn on a rod-shaped Fe-MOF. The conversions of acetone and NO reached 50% and 64%, respectively, at 240 °C. The results showed that the catalysts were capable of removing acetone and NO at the same time. Compared with the pure Fe-MOF without Co and Mn, the loaded catalysts showed a significantly higher ability to remove acetone and NO simultaneously under the combination of various factors. The key reaction steps for the catalytic conversion of acetone and NO on the catalyst surface were investigated according to the Mars-van Krevelen (MvK) mechanism, and a possible mechanism was proposed. This study presents a new idea for the simultaneous removal of acetone and NOx by photothermal coupling.

Effect of Rh Doping on Optical Absorption and Oxygen Evolution Reaction Activity on BaTiO3 (001) Surfaces

In the present work, we investigate the potential of modified barium titanate (BaTiO3), an inexpensive perovskite oxide derived from earth-abundant precursors, for developing efficient water oxidation electrocatalysts using first-principles calculations. Based on our calculations, Rh doping is a way of making BaTiO3 absorb more light and have less overpotential needed for water to oxidize. It has been shown that a TiO2-terminated BaTiO3 (001) surface is more promising from the point of view of its use as a catalyst. Rh doping expands the spectrum of absorbed light to the entire visible range. The aqueous environment significantly affects the ability of Rh-doped BaTiO3 to absorb solar radiation. After Ti→Rh replacement, the doping ion can take over part of the electron density from neighboring oxygen ions. As a result, during the water oxidation reaction, rhodium ions can be in an intermediate oxidation state between 3+ and 4+. This affects the adsorption energy of reaction intermediates on the catalyst's surface, reducing the overpotential value.

Remarkable N2-selectivity enhancement of NH3-SCR over HPMo modified MnCo-BTC@SiO2 catalyst

In this work, the phosphomolybdate (HPMo) modification strategy was applied to improve the N2 selectivity of MnCo-BTC@SiO2 catalyst for the selective catalytic reduction of NOx, and further, the mechanism of HPMo modification on enhanced catalytic performance was explored. Among MnCo-BTC@SiO2-x catalysts with different HPMo concentrations, MnCo-BTC@SiO2-0.75 catalyst exhibited not only the highest NH3-SCR performance (∼95% at 200-300°C) but also the best N2 selectivity (exceed 80% at 100-300°C) due to the appropriate redox capacity, greater surface acidity. X-ray photoelectron spectrometer (XPS) and temperature programmed reduction of H2 (H2-TPR) results showed that the modification with HPMo reduced the oxidation-reduction performance of the catalyst due to electron transfer from Mo5+ to Mn4+/Mn3+ and prevent the excessive oxidation of ammonia adsorption species. NH3 temperature-programmed desorption of (NH3-TPD) results showed that the modification with HPMo could significantly improve the surface acidity and NH3 adsorption, which enhance the catalytic activity and N2 selectivity. In-situ diffused reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) revealed that modification with HPMo increased significantly the amount of adsorbed NH3 species on the Bronsted acid site and CB/CL, it suppressed the production of N2O by inhibiting the production of NH species, the deep dehydrogenation of ammonia adsorption species. This study provided a simple design strategy for the catalyst to improve the low-temperature catalytic performance and N2 selectivity.

Rational Regulation of Reducibility and Acid Site on Mn-Fe-BTC to Achieve High Low-Temperature Catalytic Denitration Performance

Selective catalytic reduction with ammonia is the mainstream technology of flue gas denitration (de-NO_x). The reducibility and acid site are two important factors affecting the de-NO_x performance, and effective regulation between them is the key to obtain a highly efficient de-NO_x catalyst. Herein, a series of Mn-Fe-BTC with different ratios of Mn and Fe are synthesized, among which 2Mn-1Fe-BTC with 2:1 molar ratio of Mn and Fe has excellent low-temperature (LT) de-NO_x performance (above 90% NO conversion between 60 and 270 °C) and good tolerance to H₂O and SO₂ poisoning (88% NO conversion at 150 °C with 100 ppm of SO₂ and/or 6% H₂O). It is revealed that the reducibility properties and acid sites of Mn-Fe-BTC can be flexibly tuned by the ratio of Mn and Fe. The difference in electronegativity between Fe and Mn leads to the redistribution of valence electrons, which enables the controllable reducibility of Mn-Fe-BTC. Furthermore, different amounts of Mn and Fe lead to different electron transport, which determines the type and number of acid sites. The synergistic effect of Mn and Fe endows Mn-Fe-BTC with enhanced surface molecular adsorption capacity and enables the catalyst to selectively chemisorb NH₃ and NO at different active sites. This research provides guidance for the flexible regulation of reducibility and acid site of LT de-NO_x catalyst.

Effect of Solvothermal Temperature on Morphology and Supercapacitor Performance of Ni-MOF

A series of Ni-MOF materials were synthesized via a simple hydrothermal method and can be employed as electrodes for supercapacitors (SCs). Different temperatures were selected to unveil the effect of temperature on the formation, structure, and electrochemical performance of Ni-MOF-x (x = 60, 80, 100, and 120). Ni-MOF-80 possessed a larger specific surface area with a cross-network structure formed on its surface. The synthesized Ni-MOF electrode delivered a specific capacity of 30.89 mA h g^-1 when the current density reached 1 A g^-1 in a three-electrode system. The as-fabricated Ni-MOF materials could be further designed and are expected to deliver satisfactory performance in practice.

Progress in Metal-Organic Framework Catalysts for Selective Catalytic Reduction of NOx: A Mini-Review

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.

Synthesis of metal–organic frameworks (MOFs) and their application in the selective catalytic reduction of NOx with NH3

This review summarizes the synthesis, applications for the NH3-SCR and methods for strengthening the water resistance and thermal stability of MOF catalysts.