Effect of inserting Cr in promoting the deep oxidation of dichloromethane over Co/WNb catalysts at low temperatures.

Enhancing catalytic activity while inhibiting the generation of chlorine byproducts is essential in the catalytic oxidation process of chlorinated volatile organic compounds (CVOCs). In this study, Cr-modified Co/WNb catalysts were synthesized and utilized for the degradation of dichloromethane (DCM). It was found that the moderate introduction of Cr exposed more Cr6+ on the catalyst surface due to the interaction between cobalt and chromium oxides, which promoted the generation of more chemisorbed oxygen on the surface, thus improving the redox properties and enhancing the activity of the catalysts. Additionally, the introduction of Cr increased the B acid sites of the catalysts, promoting the breaking of C-Cl bonds and the removal of dissociated Cl- Meanwhile, the improved redox properties also allowed further oxidation of the dissociated activated intermediate products and inhibited the generation of chlorine byproducts. The catalyst activity was optimal when the Cr to Co molar ratio was 4, which the T90 of DCM was 256 °C and the monochloromethane selectivity was only 1.7 %. Moreover, Co4Cr/WNb showed excellent chlorine and water resistance, making it an ideal candidate for CVOC degradation.

Ordering Bimetallic Cu-Pd Catalysts onto Orderly Mesoporous SrTiO3-Crystal Nanotubular Networks for Efficient Carbon Dioxide Photoreduction.

Artificial photosynthesis of fuels has garnered significant attention, with SrTiO3 emerging as a potential candidate for photocatalysis due to its exceptional physicochemical properties. However, selectively converting CO2 into fuels with desired reaction products remains a grand challenge. Herein, we design an updated method via an aging strategy based on the electrospinning technique to synthesize a single-crystalline Al-doped SrTiO3 nanotubular networks with self-assembled orderly mesopores, further modified by Cu-Pd alloy. It exhibits both high crystallinity and superior cross-linked mesoporous structures, effectively facilitating charge carrier transfer, photon utilization, and mass transfer, with a remarkable enhancement from 0.025 mmol h-1 m-2 to 1.090 mmol h-1 m-2 in the CO production rate. Meanwhile, the ordered arrangement of Cu and Pd atoms on the (111) surface can promote the rate-determining step (*CO2 to *COOH), which is also responsible for its good activity. The presence of CuO in the reaction confers a significant advantage for CO desorption, leading to a remarkable CO selectivity of 95.54 %. This work highlights new insights into developing advanced heterogeneous photocatalysts.

Surface acid etching for efficient anchoring of potassium on 3DOM La0.8Sr0.2MnO3 catalyst: An integration strategy for boosting soot and NOx simultaneous elimination.

The emission of soot and NOx is one of the most severe environmental issues, and the key factor is the development of catalysts in after-treatment systems. In this study, an innovative non-noble metal catalyst, named HKLSM, was fabricated by etching 3DOM La0.8Sr0.2MnO3 with citric acid and synchronously anchoring potassium salt, for soot and NOx simultaneous removal. The citric acid could not only slightly erode the 3DOM skeleton, thereby beneficial to the dispersion of potassium, but also react with high-valence state Mn to generate abundant coordination unsaturated Mn3+ sites, which could produce more active oxygen species. Moreover, HKLSM showed a higher NOx adsorption capability than the samples that were not subjected to acid etching. This adsorbed NOx could be stored as NO3- species, which could facilitate soot combustion. Among all the as-prepared catalysts, HKLSM demonstrated a competitive soot combustion activity with a T50 value of 368 °C, a TOF value of 3.24 × 10-4 s-1, a reaction rate of 1.87 × 10-7 molg-1s-1, a total NOx to N2 yield of 42.0% and favorable reusability and water-resistance. This integration strategy can rationalize an alternative protocol to soot and NOx simultaneous elimination or even other catalysis systems.

Potassium promoted macro-mesoporous Co3O4-La0.88Sr0.12CoO3-δ nanotubes with large surface area: A high-performance catalyst for soot removal.

The construction of porous perovskite nanotubular materials with a good intrinsic activity, as well as a greater dispersion of the active sites is an effective strategy to obtain a high-performance catalyst used in soot removal. Thence, macro-mesoporous Co3O4-La0.88Sr0.12CoO3-δ nanotubes with large specific surface area (154.4 m2·g-1) from the acid etching of the porous La0.6Sr0.4CoO3-δ nanotubes, are supported by 5% K through bubbling method following calcination for soot combustion. The relationship between the specific surface area and K dispersion and their effect on the activity are studied by a series of isothermal kinetic measurements combined with the characterizations and activity evaluation results. It can be found that the greater the amount is of K+ incorporated into perovskite lattice, the better the dispersion of K, as well as the La2O2CO3 formed on the catalyst surface, thus leading to the enhanced performance in the soot catalytic combustion. As a result, the 5% K supported macro-mesoporous Co3O4-La0.88Sr0.12CoO3-δ nanotubes after acid etching show good activity and stability, where the T50 is 338 °C (5% O2 + 500 ppm NO + 6% H2O) with a good CO2 selectivity (above 99%), the activate energy is 78.1 kJ·mol-1, and the turnover frequency is 5.14 × 10-4 s-1.

Surface engineering on porous perovskite-type La0.6Sr0.4CoO3-δ nanotubes for an enhanced performance in diesel soot elimination.

The porous perovskite-type La0.6Sr0.4CoO3-δ nanotubes are synthesized by sol-gel method combined with electrospinning technique following the calcination, while the porous nanotubular structure can increase the utilization of active sites related to the catalytic activity in soot oxidation. In order to further improve the catalytic activity, porous La0.6Sr0.4CoO3-δ nanotubes are further treated with nitric acid to obtain a larger specific surface area in this work. The as-prepared catalysts are characterized by different techniques to study their physical and chemical properties. The soot catalytic activity is evaluated by the temperature programmed oxidation tests and the values of activation energy. Based on the characterizations and catalytic activity evaluation, the correlation between the specific surface area and catalytic activity is well revealed by the isothermal kinetic measurements. The higher specific surface area (more than 150.0 m2 g-1) contributes to a larger amount and a better dispersion of the active oxygen species, thence improving the catalytic activity of soot oxidation. As a result, porous perovskite-type La0.6Sr0.4CoO3-δ nanotubes after nitric acid treatment for 4 h have the best activity and a good stability, with the T50 of 442 °C (5% O2) and 415 °C (5% O2 + 500 ppm NO), and the Ea of 93.6 kJ mol mol-1.

MnO x dispersed on attapulgite derived Al-SBA-15: a promising catalyst for volatile organic compound combustion.

To improve the catalytic activity when utilizing metal oxides for the combustion of VOCs, Mn/Al-SBA-15 catalysts have been successfully synthesized through an emerging wetness impregnation technique involving Mn(NO3)2 on Al-SBA-15, which has been directly prepared from attapulgite by a hydrothermal method. Compared to Mn/SBA-15, which is prepared with TEOS as its silicon source, all the as-prepared Mn/Al-SBA-15 catalysts demonstrated enhanced catalytic performance in the oxidation of toluene. From this research, the 8% Mn/Al-SBA-15 catalyst presented the best catalytic performance, due to the high efficiency resulting from the high chemical valence of Mn4+. When the concentration of toluene was 2000 ppm, and the space velocity was 60 000 mL (g h)-1, 8% Mn/Al-SBA-15 could effectively reduce the T 50 and T 90 values of toluene to 201 and 278 °C, respectively; while the 8% Mn/SBA-15 catalyst could reduce the T 50 and T 90 values of toluene to 223 and 298 °C, respectively. A systematic investigation has been conducted to reveal the synergistic effects of Al doping and manganese loading on the enhanced catalytic performance. The experiments showed impressive results, demonstrating that Al doping can not only increase the surface acidity of SBA-15, but it can also be beneficial for achieving a uniform dispersion of MnO x on the surface and in the pores of Al-SBA-15, resulting in the enhancement of the catalytic performance.

Surface engineering of a chromium metal-organic framework with bifunctional ionic liquids for selective CO2 adsorption: Synergistic effect between multiple active sites.

Targeting CO2 capture application, a new strategy for building multiple adsorption sites in metal-organic framework MIL-101(Cr) was constructed through the incorporation of diethylenetriamine-based ionic liquid (DETA-Ac) via a post-synthetic modification approach. The DETA-Ac, with multi-amine-tethered cation and acetate anion, could not only provide additional binding sites, but also enhance the affinity of framework surfaces toward CO2. Simultaneously, the high surface area and large cage size of MIL-101(Cr) ensured the better dispersion of IL, thus exposing more active sites for CO2 adsorption. In addition, enough free space was still retained after functionalization, which facilitated CO2 transport and allowed the Cr(III) sites deep within the pores to be accessed. The multiple adsorption sites originating from IL and MOF were found to synergistically affect the CO2 capture performance of the composite. The adsorption capacity and selectivity of DETA-Ac@MIL-101(Cr) for CO2 were significantly improved. The higher isosteric heats of adsorption (Qst) evidenced the stronger interaction between the composite and CO2 molecules. Moreover, a possible two-step mechanism was proposed to reveal the manner in which CO2 bound to the IL-incorporated frameworks. Despite the relatively high initial Qst value, the DETA-Ac@MIL-101(Cr) could be easily regenerated with almost no drop in CO2 uptake during six cycles.

Template-directed fabrication of MIL-101(Cr)/mesoporous silica composite: Layer-packed structure and enhanced performance for CO2 capture.

A novel hybrid material constituted of MIL-101(Cr) and mesoporous silica was successfully assembled through an in-situ hydrothermal method. The MCM-41 with well-ordered mesopores acted as the structure-directing agent, which regulated the growth of MIL-101(Cr) crystals along a certain direction and restricted the expansion of framework. Meanwhile, the hydroxyl groups existed in MCM-41 preferentially coordinated with the Cr3+ centers in MOF, followed by the layer-packed arrangement of MIL-101(Cr) nanocrystals on the surface of matrix. The structural characterizations further revealed that the introduction of MCM-41 could increase the micropore volume and specific surface area. The MIL-101(Cr)@MCM-41 exhibited higher CO2 uptake capacity and adsorption rate compared with the original MIL-101(Cr) at 298 K and 1 bar. Via ideal adsorbed solution theory (IAST), it could be further predicted that the composite was more inclined to adsorb CO2 than N2. The calculated isosteric heats of CO2 adsorption and desorption activation energy demonstrated that the interaction between CO2 molecules and the composite was also enhanced. The as-prepared MIL-101(Cr)@MCM-41 showed good reusability and could be easily regenerated without any reduction in its CO2 adsorption capacity. Hence, this study opened up a new pathway for designing hierarchical porous structured MOF-based materials with advanced gas separation performance.

Synthesis of Hierarchically Structured Hybrid Materials by Controlled Self-Assembly of Metal-Organic Framework with Mesoporous Silica for CO2 Adsorption.

The HKUST-1@SBA-15 composites with hierarchical pore structure were constructed by in situ self-assembly of metal-organic framework (MOF) with mesoporous silica. The structure directing role of SBA-15 had an obvious impact on the growth of MOF crystals, which in turn affected the morphologies and structural properties of the composites. The pristine HKUST-1 and the composites with different content of SBA-15 were characterized by XRD, N2 adsorption-desorption, SEM, TEM, FT-IR, TG, XPS, and CO2-TPD techniques. It was found that the composites were assembled by oriented growth of MOF nanocrystals on the surfaces of SBA-15 matrix. The interactions between surface silanol groups and metal centers induced structural changes and resulted in the increases in surface areas as well as micropore volumes of hybrid materials. Besides, the additional constraints from SBA-15 also restrained the expansion of HKUST-1, contributing to their smaller crystal sizes in the composites. The adsorption isotherms of CO2 on the materials were measured and applied to calculate the isosteric heats of adsorption. The HS-1 composite exhibited an increase of 15.9% in CO2 uptake capacity compared with that of HKUST-1. Moreover, its higher isosteric heats of CO2 adsorption indicated the stronger interactions between the surfaces and CO2 molecules. The adsorption rate of the composite was also improved due to the introduction of mesopores. Ten cycles of CO2 adsorption-desorption experiments implied that the HS-1 had excellent reversibility of CO2 adsorption. This study was intended to provide the possibility of assembling new composites with tailored properties based on MOF and mesoporous silica to satisfy the requirements of various applications.