Promotional effects of Nb5+ and Fe3+ co-doping on catalytic performance and SO2 resistance of MnOx-CeO2 low-temperature denitration catalyst.

As we know, SO2 can cause MnOx-CeO2 (MnCeOx) catalyst poisoning, which seriously shortens the service life of the catalyst. Therefore, to enhance the catalytic activity and SO2 tolerance of MnCeOx catalyst, we modified it by Nb5+ and Fe3+ co-doping. And the physical and chemical properties were characterized. These results illustrate that the Nb5+ and Fe3+ co-doping can optimally improve the denitration activity and N2 selectivity of MnCeOx catalyst at low temperature by improving its surface acidity, surface adsorbed oxygen as well as electronic interaction. What's more, NbOx-FeOx-MnOx-CeO2 (NbFeMnCeOx) catalyst possesses an excellent SO2 resistance due to less SO2 being adsorbed and the ammonium bisulfate (ABS) formed on its surface tends to decompose, as well as fewer sulfate species formed on its surface. Finally, the possible mechanism that Nb5+ and Fe3+ co-doping enhances the SO2 poisoning resistance of MnCeOx catalyst is proposed.

Influence of phosphorus on the NH3-SCR performance of CeO2-TiO2 catalyst for NOx removal from co-incineration flue gas of domestic waste and municipal sludge.

Domestic waste and municipal sludge are two major solid hazardous substances generated from human daily life. Co-incineration technology is regarded as an effective method for the treatment of them. However, the emitted NOx-containing exhaust with high content of phosphorus should purified strictly. CeO2-TiO2 is a promising catalyst for removal of NOx by NH3-SCR technology, but the effect of phosphorous in the exhaust is ambiguous. Therefore, the effect of phosphorus on NH3-SCR performance and physicochemical properties of CeO2-TiO2 catalyst was investigated in our present work. It was found that phosphorus decreased the NH3-SCR activity below 300 °C. Interestingly, it suppressed the formation of NOx and N2O caused by NH3 over-oxidation above 300 °C. The reason might be that phosphorus induced Ti4+ to migrate from CeO2-TiO2 solid solution and form crystalline TiO2, which led to the destruction of Ti-O-Ce structure in the catalyst. So, the transfer of electrons between Ti and Ce ions, the relative contents of Ce3+, and surface adsorbed oxygen, as well as the redox performance were limited, which further inhibited the over-oxidation of NH3. In addition, phosphorus weakened the NH3 adsorption on Lewis acid sites and the adsorption performance of NO + O2, while increased the Brønsted acid sites. Finally, the reaction mechanism over CeO2-TiO2 catalyst did not change after introducing phosphorus, L-H and E-R mechanisms co-existed on the surface of the catalysts.

Insights into the co-doping effect of Fe3+ and Zr4+ on the anti-K performance of CeTiOx catalyst for NH3-SCR reaction.

A novel K-resistant Fe3+ and Zr4+ co-doped CeTiOx catalyst was first prepared by co-precipitation method for the ammonia-selective catalytic reduction (NH3-SCR) of NOx. On the premise of retaining the outstanding catalytic activity of CeTiOx catalyst, Fe3+ and Zr4+ co-doping efficiently improves its K-resistance with superior NOx conversion up to 84% after K-poisoning. Specially, the grain growth during the second calcination after K poisoning is successfully inhibited by Fe3+ and Zr4+ co-doping. Consequently, the large specific surface area with increased acid sites and efficiently retained reducibility over K-poisoned FeZrCeTiOx catalyst are realized, which prompt NH3 activation and NO oxidation, further benefit NH3-SCR. Besides, NH3-SCR reaction over CeTiOx and FeZrCeTiOx catalysts follows a possible L-H mechanism, and K-poisoning makes no change to it. Finally, a reasonable anti-K poisoning mechanism of FeZrCeTiOx catalyst is proposed: the excellent K-resistance is attributed to part of Fe and Zr are sacrificed to form Fe-O-K and Zr-O-K species protecting the active site Ce-O-Ti from K-poisoning, as well as the additional reducibility and surface acidity brought from Fe-O species with Zr prompting its uniform distribution.

Enhancing the K resistance of CeTiOx catalyst in NH3-SCR reaction by CuO modification.

It is generally accepted that CeTiOx catalyst owns outstanding catalytic activity for ammonia-selective catalytic reduction (NH3-SCR), but the tolerance to alkali metals is still dissatisfactory. Thus, it is of great importance to further elevate the catalytic activity and resistance to alkali metals of CeTiOx catalyst. In our work, a series of CeTiOx, CuO/CeTiOx, K-CeTiOx and K-CuO/CeTiOx catalysts were prepared to comprehensively analyze the influence of CuO modification on the physicochemical features, catalytic activity and anti-K ability of CeTiOx catalyst. The results manifest that CuO modification effectively enhances low-temperature catalytic activity and anti-K poisoning ability of CeTiOx catalyst by protecting the reduction ability and the surface acidity as well as weakening the adsorption strength of NOx.

Impact of the COVID-19 pandemic and control measures on air quality and aerosol light absorption in Southwestern China.

China has been performing nationwide social lockdown by releasing the Level 1 response to major public health emergencies (RMPHE) to struggle against the COVID-19 (SARS-CoV-2) outbreak since late January 2020. During the Level 1 RMPHE, social production and public transport were maintained at minimal levels, and residents stayed in and worked from home. The universal impact of anthropogenic activities on air pollution can be evaluated by comparing it with air quality under such extreme conditions. We investigated the concentration of both gaseous and particulate pollutants and aerosol light absorption at different levels of (RMPHE) in an urban area of southwestern China. During the lockdown, PM2.5, PM10, SO2, NOx, and BC decreased by 30-50%, compared to the pre-Level 1 RMPHE period. Meanwhile, the decrease of NOx caused the rise of O3 by up to 2.3 times due to the volatile organic compounds (VOCs) limitation. The aerosol light absorption coefficient at multiple wavelengths decreased by 50%, and AAE decreased by 20% during the Level 1 RMPHE. BrC played essential roles in light absorption after the RMPHE was announced, accounting for 54.0% of the aerosol absorption coefficient at 370 nm. Moreover, the lockdown down-weighted the fraction of fossil fuel in BC concentrations to 0.43 (minima). This study characterizes air pollution at the most basic level and can provide policymakers with references for the "baseline."

Characteristics and potential exposure risks of environmentally persistent free radicals in PM2.5 in the three gorges reservoir area, Southwestern China.

Environmentally persistent free radicals (EPFRs) are a novel class of hazardous substances that can exist stably in airborne particles for a period ranging from days to weeks and are potentially toxic to human health. Electron paramagnetic resonance spectroscopy (EPR) was used to characterize particulate EPFRs in Wanzhou in the Three Gorges Reservoir area in 2017. During the whole of 2017, the average concentration of particulate EPFRs was 7.0 × 1013 ± 1.7 × 1013 spins/m3. The seasonal concentration of EPFRs in PM2.5 showed a trend of autumn > winter > spring > summer. The maxima and minima of EPFRs occurred in spring with concentrations of 2.1 × 1014 spins/m3 and 9.4 × 1012 spins/m3 respectively. The EPFRs in PM2.5 were mainly carbon-centered radicals with adjacent oxygen atoms. Significant positive correlations were found between EPFRs and SO42-, NO3- and NH4+ (r > 0.55, n = 111), indicating that EPFRs are associated with secondary sources. The atmospheric processing of particles from coal combustion, traffic, and agriculture were important sources of EPFRs. They were also particularly well correlated with K+ and Cl- in winter, suggesting that EPFRs may also be derived from wintertime biomass burning emissions. The amount of inhalable EPFRs in Wanzhou was equivalent to the range of 2.3-6.8 cigarettes per capita per day. This study provides evidence of the potential health risks of EPFRs in PM2.5, and references for air pollution control in the Three Gorges Reservoir area.

Brown carbon aerosol in two megacities in the Sichuan Basin of southwestern China: Light absorption properties and implications.

The light absorption of brown carbon (BrC) makes a significant contribution to aerosol light absorption (Abs) and affects the radiative forcing. In this study, we analyzed and evaluated the light absorption and radiative forcing of BrC samples collected from December 2016 to January 2017 in Chongqing and Chengdu in the Sichuan Basin of Southwest China. Based on a two-component model, we estimated that BrC light absorption at 405 nm was 19.9 ± 17.1 Mm-1 and 19.2 ± 12.3 Mm-1 in Chongqing and Chengdu, contributing 19.0 ± 5.0% and 17.8 ± 3.7% to Abs respectively. Higher Abs405,BrC, MAE405,BrC, and AAE405-980 values were observed during the pollution period over the clean period in both cities. The major sources of BrC were biomass burning (BB) and secondary organic aerosol in Chongqing, and coal combustion (CC) and secondary organic aerosol in Chengdu. During the pollution period, aged BrC formed from anthropogenic precursors via its aqueous reactions with NH4+ and NOx had impacts on BrC absorption in both cities. BB led to higher Abs405,BrC, MAE405,BrC, and AAE405-980 values in Chongqing than Chengdu during the pollution period. The fractional contribution of radiation absorbed by BrC relative to BC in the wavelengths of 405-445 nm was 60.2 ± 17.0% and 64.2 ± 11.6% in Chongqing and Chengdu, significantly higher than that in the range of 405-980 nm (26.2 ± 6.7% and 27.7 ± 4.6% respectively) (p < 0.001). This study is useful for understanding the characterization, sources, and impacts of BrC in the Sichuan Basin.

Effect of precursors on the structure and activity of CuO-CoOx/γ-Al2O3 catalysts for NO reduction by CO.

Catalytic reduction of NO by CO was studied over a series of CuO-CoOx/γ-Al2O3 catalysts prepared by co-impregnation with different copper and cobalt precursors (acetate and nitrate) to evaluate the structure-activity relationship. The obtained samples were characterized in detail by means of XRD, LRS, XPS, H2-TPR and in situ FT-IR technologies. Results indicate that copper oxide is agglomerated while cobalt oxide is dispersed on γ-Al2O3 for the catalyst prepared from copper acetate and cobalt acetate precursors (CuACoA); CuxCo3-xO4 spinel is formed and agglomerated on the catalyst prepared from copper nitrate and cobalt nitrate precursors (CuNCoN); while both copper oxide and cobalt oxide could be homogeneously dispersed for the catalyst prepared from copper nitrate and cobalt acetate precursors (CuNCoA), which exhibits the best activity for NO reduction by CO. Probably the synergistic effect between dispersed copper oxide and cobalt oxide is propitious to the oxygen transfer, which could be the reason for its high activities. Finally, a possible reaction mechanism was tentatively proposed to explore the different catalytic performances in NO reduction by CO model reaction.

Improved low temperature NH3-SCR performance of FeMnTiO(x) mixed oxide with CTAB-assisted synthesis.

FeMnTiOx mixed oxide is prepared by the CTAB-assisted co-precipitation method, and the transformation of anatase into rutile is inhibited by CTAB to some extent. The catalyst obtained in the present work shows nearly 100% NO conversion at 100-350 °C, more than 80% N2 selectivity at 75-200 °C, and excellent H2O durability for the selective catalytic reduction of NO by NH3 with a space velocity of 30,000 mL g(-1) h(-1).

Tailoring copper valence states in CuOδ/γ-Al2O3 catalysts by an in situ technique induced superior catalytic performance for simultaneous elimination of NO and CO.

An in situ technique is employed to tailor the valence states of copper in CuOδ/γ-Al2O3 catalysts with the purpose of inducing superior catalytic performance for simultaneous elimination of NO and CO. The catalyst with zero-valent copper exhibits excellent catalytic performance, which is comparable with the conventional supported noble-metal catalysts.

Investigation of surface synergetic oxygen vacancy in CuO-CoO binary metal oxides supported on γ-Al2O3 for NO removal by CO.

The influence of CO pretreatment on the properties of CuO-CoO/γ-Al(2)O(3) catalysts was investigated by SEM, TEM, XRD, LRS, XPS, TPR, and in situ FT-IR techniques. And the activities were measured by NO removal by CO. It was shown that the CuO-CoO/γ-Al(2)O(3) catalysts following CO pretreatment exhibited extremely high activity and selectivity. The interaction between copper oxide and cobalt oxide upon the γ-Al(2)O(3) support before and after CO pretreatment was tentatively discussed in the view of incorporation model. According to this model, the dispersed Cu-O-Co species could be reduced to Cu-□-Co species by CO pretreatment, which was considered to be the primary active component for this reaction. FT-IR results suggested that CO was apt to adsorb on Cu(+) sites rather than Co(2+) while the NO adsorbates could convert to much more stable species with the temperature increasing. Undoubtedly, it was the surface synergetic oxygen vacancy coupled with the adjacent Cu and Co ions that guaranteed the reaction well processing over the CO pretreated samples. As a result, a possible mechanism was tentatively proposed.