Yinghao Chu

Oxidation of SO2 and NO by epoxy groups on graphene oxides: the role of the hydroxyl group

Simultaneous catalytic removal of SO2 and NOx at low temperature (<150 °C) has long been recognized as a challenge for the treatment of coal-burned flue gases. Density functional theory corrected with dispersion was used to investigate the potential of graphene oxides (GOs) for the catalytic oxidation of SO2 and NOx. It is found that both the SO2 and NOx can be oxidized by epoxy groups of GO nearly at room temperature. The hydroxyl groups on the GO surface enhance the adsorption and oxidation of SO2, and of NO as well, but in quite different ways. For the case of SO2, the promotion is derived from the formation of charge transfer channels, which are fabricated by the hydroxyl group, the adsorbed SO2 and the epoxy group. The promotion is enhanced by the introduction of more hydroxyl groups as more charge transfer channels are formed. However, for NO, the hydroxyl group leads to a strong N–C covalent interaction between the adsorbed NO molecules and the GO surface, through which the NO is activated and oxidized with a much lower barrier. These results provide a mechanistic explanation of the low temperature catalytic oxidation of SO2 and NO by carbon materials and insights into designing new carbon-based catalysts.

Effects of preparation conditions on Mn-based activated carbon catalysts for desulfurization

A series of Mn-based activated carbon catalysts were prepared by excessive impregnation with or without ultrasonic assistance, and manganese (Mn) species and surface chemical properties of catalysts before and after SO2 removal were studied. The results showed that different preparation conditions significantly influence the desulfurization activity of Mn-based activated carbon catalysts. The breakthrough sulfur capacity of 5FMn/ACA36 prepared by ultrasonic assisted excessive impregnation is 73.0 mg g−1, while that of 5FMn/ACN36 increases to 126.1 mg g−1. The catalysts exhibit different desulfurization activities when carbon carriers are pretreated with nitric acid at different concentrations, and with the increase of concentrations, the breakthrough sulfur capacity of catalysts increases from 118.1 to 141.6 mg g−1. Catalysts calcined at different temperatures show different desulfurization activities. Both 5FMn/ACW and 5Mn/ACW calcined at 800 °C have the best desulfurization activity, but 5FMn/ACN36 and 5Mn/ACN36 calcined at 650 and 800 °C are similar. The optimal loading of catalysts prepared by excessive impregnation is 7%, but that of catalysts prepared by ultrasonic assisted excessive impregnation is 0.5%. Nitric acid pretreatment can change surface chemical properties and reduce the formation temperature as well as the crystalline size of Mn oxide species such as MnO and Mn3O4. The introduction of ultrasonic oscillation cannot change active species and oxygen-containing functional groups (such as C–O, CO and OC–OH) but reduce the active component content to enhance the activity. Mn loading influences the content of active components and oxygen-containing functional groups on carbon supports, leading to a different desulfurization activity. After SO2 removal, MnO, Mn2O3 and Mn3O4 are still observed, but some of them transform into MnO2 with low crystallinity, and some react with generated H2SO4 to form MnSO4, resulting in catalyst deactivation. Types of oxygen-containing functional groups after SO2 removal remain the same but the relative contents decrease, showing that they participate in the reaction of SO2 removal.

Influence of Ni Species of Ni/AC Catalyst on Its Desulfurization Performance at Low Temperature

Abstract A series of Ni/AC catalyst samples were prepared by excessive impregnation, and the desulfurization activity of Ni/AC calcined at different temperatures was investigated. The Ni species on the Ni/AC catalyst calcined at different temperatures were studied by X-ray diffraction and X-ray photoelectron spectroscopy. The characterization results showed that the Ni species on the catalyst calcined at 400 °C is Ni 2 O 3 . After calcination at 550 °C, NiO species is formed on the activated carbon. NiO and Ni coexist on the Ni/AC catalyst calcined at 800 °C, and only pure Ni species is observed after calcination at 1000 °C. This suggested that Ni can form different chemical states on the Ni/AC catalyst calcined at different temperatures. The desulfurization test results showed that the catalysts calcined at 550 and 800 °C exhibit good desulfurization activity, whereas the catalyst calcined at 400 °C has poor activity, indicating that different chemical states of Ni on the Ni/AC catalyst show different desulfurization performance, and NiO is the main active phase of the Ni/AC catalyst.

Low temperature selective catalytic reduction of NO by C3H6 over CeOx loaded on AC treated by HNO3

Abstract The activated carbons from coal were treated by HNO 3 (named as NAC) and used as carriers to load 7% Ce (named as Ce(0.07)/NAC) by impregnation method. The physical and chemical properties were investigated by thermogravimetric-differential thermal analysis (TG-DTA), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), scanning electron microscopy (SEM) and NH 3 -temperature programmed desorption (NH 3 -TPD) and NO-temperature programmed desorption techniques. The catalytic activities of Ce(0.07)/NAC were evaluated for the low temperature selective catalytic reduction (SCR) of NO with C 3 H 6 using temperature-programmed reaction (TP-reaction) in NO, C 3 H 6 , O 2 and N 2 as a balance. The results showed that the specific surface area of Ce(0.07)/NAC was 850.8 m 2 /g and less than NAC, but Ce oxides could be dispersed highly on the activated carbons. Ce oxides could change acid sites and NO adsorption as well as oxygen-containing functional groups of activated carbons, and Ce 4+ and Ce 3+ coexisted in catalysts. The conversion of NO with C 3 H 6 achieved 70% at 280 °C over Ce(0.07)/NAC, but with the increase of O 2 concentration, heat accumulation and nonselective combustion were exacerbated, which could cause surface ashing and roughness, resulting in a sharp decrease of catalytic activities. The optimum O 2 concentration used in the reaction system was 3% and achieved the high conversion of NO and the widest temperature window. The conversion of NO was closely related to the NO concentrations and [NO]/[C 3 H 6 ] ratios, and the stoichiometric number was just close to 2:1, but the presence of H 2 O could affect the denitration efficiency of catalyst.

Dissociation of O2 and its reactivity on O/S doped graphene

It is routinely believed that the oxidation of SO2 to SO3 dominates the removal rate of SO2 on carbon-based catalysts. Recently, both experiment and theoretical calculations evidence that SO2 is readily oxidized by epoxy groups on graphene oxides at room temperature. Based on this fact, we hypothesize in this study that the real rate-determining step for SO2 catalytic oxidation under O2 atmosphere could be the dissociation of molecular O2, which further forms oxygen functional groups on the graphene surface. Density functional theory corrected with dispersion was employed to investigate the dissociation of O2 on O or S doped graphene and then its reactivity for SO2 oxidation. The results showed that O/S doping greatly promotes the dissociation, which leads to the formation of epoxy and/or carbonyl groups on the graphene surface. However, a high oxidation barrier for the oxidation of SO2 by the carbonyl group was found, which implies that the carbonyl group is of low reactivity. Therefore, dopant screening or the design of doped structures should be carefully considered to avoid the formation of carbonyl during O2 dissociation.

Influence of Fe loadings on desulfurization performance of activated carbon treated by nitric acid

ABSTRACT A series of Fe supported on activated carbon treated by nitric acid are prepared by incipient wetness impregnation with ultrasonic assistance and characterized by N2 adsorption–desorption, X-ray diffraction, Fourier transform infrared spectrum and X-ray photoelectron spectroscopy. It has shown that Fe loadings significantly influence the desulfurization activity. Fe/NAC5 exhibits an excellent removal ability of SO2, corresponding to breakthrough sulfur capacity of 323 mg/g. With the increasing Fe loadings, the generated Fe3O4 and Fe2SiO4 increase, but Fe2(SO4)3 is observed after desulfurization. Fe/NAC1 has a Brunauer–Emmett–Teller (BET) surface area of 925 m2/g with micropore surface area of 843 m2/g and total pore volume of 0.562 cm3/g including a micropore volume of 0.300 cm3/g. With the increasing Fe loadings, BET surface area and micropore volume decrease, and those of Fe/NAC10 decrease to 706 m2/g and 0.249 cm3/g. The Fe loadings influence the pore-size distribution, and SO2 adsorption mainly reacts in micropores at about 0.70 nm. C=O and C–O are observed for all samples before SO2 removal. After desulfurization, the C–O stretching is still detected, but the C=O stretching vibration of carbonyl groups disappears. The stretching of S–O or S=O in sulfate is observed at 592 cm−1 for the used sample, proving that the existence of .