Selective catalytic oxidation reaction of p -xylene on manganese–iron mixed oxide materials

Potential Strategy to Control the Organic Components of Condensable Particulate Matter: A Critical Review

More and more attention has been paid to condensable particulate matter (CPM) since its emissions have surpassed that of filterable particulate matter (FPM) with the large-scale application of ultralow-emission reform. CPM is a gaseous material in the flue stack but instantly turns into particles after leaving the stack. It is composed of inorganic and organic components. Organic components are an important part of CPM, and they are an irritant, teratogenic, and carcinogenic, which triggers photochemical smog, urban haze, and acid deposition. CPM organic components can aggravate air pollution and climate change; therefore, consideration should be given to them. Based on existing methods for removing atmospheric organic pollutants and combined with the characteristics of CPM organic components, we provide a critical overview from the aspects of (i) fundamental cognition of CPM, (ii) common methods to control CPM organic components, and (iii) catalytic oxidation of CPM organic components. As one of the most encouraging methods, catalytic oxidation is discussed in detail, especially in combination with selective catalytic reduction (SCR) technology, to meet the growing demands for multipollutant control (MPC). We believe that this review is inspiring for a fuller understanding and deeper exploration of promising approaches to control CPM organic components.

p-Xylene Oxidation to Terephthalic Acid: New Trends

Large-scale terephthalic acid production from the oxidation of p-xylene is an especially important process in the polyester industry, as it is mainly used in polyethylene terephthalate (PET) manufacturing, a polymer that is widely used in fibers, films, and plastic products. This review presents and discusses catalytic advances and new trends in terephthalic acid production (since 2014), innovations in terephthalic acid purification processes, and simulations of reactors and reaction mechanisms.

Enhanced photocatalytic degradation of xylene by blackening TiO2 nanoparticles with high dispersion of CuO

To enhance the photocatalytic activity of TiO₂, a new preparation method has been proposed to synthesize the catalysts by introducing Cu-MOF as a precursor and performing a blackening process via a mixture with NaBH₄ for TiO₂ nanoparticles (CuO-TiO₂(mb)). The results showed that the removal efficiency of xylene under ultraviolet and visible light over CuO-TiO₂(mb) was 3.45 times higher than that of the catalysts prepared by impregnation of CuO on the surfaces of TiO₂ (CuO-TiO₂(d)) and 12.12 times higher than that of pure TiO₂ nanoparticles. Analyses by the X-ray diffraction, scanning electron microscopy, and transmission electron microscopy indicated that the introduction of Cu-MOF as a precursor on the surface of the catalyst resulted in CuO-TiO₂(mb) presenting a lower grain size compared with TiO₂ nanoparticles and CuO-TiO₂(d). The results of X-ray photoelectron spectroscopy, diffuse reflectance spectrum and photoluminescence indicated that blackening process narrowed the bind gap width and shortened the band gap from 2.95 eV to 1.32 eV, introduced the coexistence of Ti⁴⁺, Ti³⁺, Cu²⁺ and Cu⁺ in CuO-TiO₂(mb) decreased the recombination rate of e^--h⁺, which greatly improved the light response of CuO-TiO₂(mb) under ultraviolet and visible light, resulting in the benefit to the photocatalytic reaction.

Efficient catalytic oxidation of methyl aromatic hydrocarbon with N-alkyl pyridinium salts

A series of N-alkyl pyridinium salts were synthesized and employed as metal-free catalyst for the selective oxidation of methyl aromatic hydrocarbon with molecular oxygen. The electronic effect of the substitutes was found to be an important factor for the catalytic performance. With the introduction of electron-donating substitute –N(CH₃)₂, the conversion of p-xylene and selectivity of p-toluic acid could be simultaneously increased. 1-Benzyl-4-N,N-dimethylaminopyridinium salt showed the highest catalytic activity, and 95% conversion with 84% of selectivity to p-toluic acid could be obtained for the selective oxidation of p-xylene. Several methyl aromatic hydrocarbons could all be efficiently oxidized with the reported catalyst at the absence of any metal species.

A series of N-alkyl pyridinium salts were synthesized and employed as metal-free catalyst for the selective oxidation of methyl aromatic hydrocarbon with molecular oxygen.

Low Temperature deNOx Catalytic Activity with C2H4 as a Reductant Using Mixed Metal Fe-Mn Oxides Supported on Activated Carbon

The selective catalytic reduction of NOx (deNOx) at temperatures less than or at 200 °C was investigated while using C2H4 as the reductant and mixed oxides of Fe and Mn supported on activated carbon; their activity was compared to that of MnOx and FeOx separately supported on activated carbon. The bimetallic oxide compositions maintained high NO conversion of greater than 80–98% for periods that were three times greater than those of the supported monometallic oxides. To examine potential reasons for the significant increases in activity maintenance, and subsequent deactivation, the catalysts were examined by using bulk and surface sensitive analytical techniques before and after catalyst testing. No significant changes in Brunauer-Emmett-Teller (BET) surface areas or porosities were observed between freshly-prepared and tested catalysts whereas segregation of FeOx and MnOx species was readily observed in the mono-oxide catalysts after reaction testing that was not detected in the mixed oxide catalysts. Furthermore, x-ray diffraction and Raman spectroscopy data detected cubic Fe3Mn3O8 in both the freshly-prepared and reaction-tested mixed oxide catalysts that were more crystalline after testing. The presence of this compound, which is known to stabilize multivalent Fe species and to enhance oxygen transfer reactions, may be the reason for the high and relatively stable NO conversion activity, and its increased crystallinity during longer-term testing may also decrease surface availability of the active sites responsible for NO conversion. These results point to a potential of further enhancing catalyst stability and activity for low temperature deNOx that is applicable to advanced SCR processing with lower costs and less deleterious side effects to processing equipment.

Performance of C2H4 Reductant in Activated-Carbon- Supported MnOx-based SCR Catalyst at Low Temperatures

Hydrocarbons as reductants show promising results for replacing NH3 in SCR technology. Therefore, considerable interest exists for developing low-temperature (<200 °C) and environmentally friendly HC-SCR catalysts. Hence, C2H4 was examined as a reductant using activated-carbon-supported MnOx-based catalyst in low-temperature SCR operation. Its sensitivity to Mn concentration and operating temperature was parametrically studied, the results of which showed that the catalyst activity followed the order of 130 °C > 150 °C > 180 °C with an optimized Mn concentration near 3.0 wt.%. However, rapid deactivation of catalytic activity also occurred when using C2H4 as the reductant. The mechanism of deactivation was explored and is discussed herein in which deactivation is attributed to two factors. The manganese oxide was reduced to Mn3O4 during reaction testing, which contained relatively low activity compared to Mn2O3. Also, increased crystallinity of the reduced manganese and the formation of carbon black occurred during SCR reaction testing, and these constituents on the catalyst’s surface blocked pores and active sites from participating in catalytic activity.