Xiaojin Han

Promoting role of sulfur groups in selective catalytic reduction of NO with NH3 over H2SO4 modified activated carbons

To determine the role of sulfur groups formed on activated carbon (AC) in the selective catalytic reduction (SCR) of NO with NH3, coal-based AC was modified by H2SO4 under various conditions and then treated in N2 atmosphere at 400 °C. The resulting carbons were characterized by N2 adsorption, elemental analysis, temperature programmed desorption and X-ray photoelectron spectroscopy, and tested for the SCR of NO with NH3 in the temperature range of 30–250 °C. Results reveal that H2SO4 modification has little effect on the textural properties, but promotes the formation of sulfur and oxygen groups. The sulfur groups incorporated by H2SO4 modification are mainly sulfonic groups and then sulfates. In particular, these sulfur groups play a predominant role in improving NH3 adsorption and then enhancing the SCR activity of modified carbons above 150 °C. However, the contribution of oxygen groups to NO reduction is very limited under the conditions employed in this work.

Using vanadyl sulfate to prepare carbon-supported vanadium catalyst for flue gas desulfurization

Abstract Vanadyl sulfate (V IV OSO 4 ) was used to prepare carbon-supported vanadium catalyst for flue gas desulfurization. The V IV OSO 4 impregnated on activated carbon (AC) was easily oxidized into vanadium(V) sulfate phase (possibly V 2 O 3 (SO 4 ) 2 ) in air, which exhibited high catalytic activity toward SO 2 oxidation, thus significantly enhancing SO 2 retention on AC. Furthermore, the vanadium(V) sulfate can be decomposed upon calcination in nitrogen with optimum temperature of 500?C to form vanadium(V) oxide, further improving SO 2 retention mainly due to increase in micropore volume suitable for sulfate storage and showing suitability of vanadyl sulfate to prepare traditional V 2 O 5 /AC catalyst. To obtain fully oxidized vanadium oxides, preoxidation was carried out on catalyst after calcination. However, due to ablation of carbon support, reduction of vanadium and/or formation of surface oxygen groups, the preoxidation was negative for SO 2 retention. Additionally, this paper provided preliminary evidence indicating transformation of vanadium(V) oxide in V 2 O 5 /AC into vanadium(V) sulfate during desulfurization. Combined with catalytic role of vanadium(V) sulfate for SO 2 oxidation, SO 2 removal on V 2 O 5 /AC likely followed a mechanism that the vanadium(V) oxide firstly transformed into vanadium(V) sulfate and the latter was then responsible for subsequent SO 2 oxidation into H 2 SO 4 .

Study of SO2 oxidation over V2O5/activated carbon catalyst using in situ diffuse reflectance infrared Fourier transformation spectroscopy

The SO2 oxidation over V2O5/AC catalyst was studied using an in situ diffuse reflectance infrared Fourier transformation spectroscopy technique at 120 °C. Results reveal that the surface oxygen groups could neither act as active sites for SO2 oxidation nor supply the oxygen needed for VV↔VIV redox cycle. The vanadia species and gas phase oxygen are essential for SO2 oxidation. During SO2 oxidation over V2O5/AC, the surface hydroxyl groups involve in the formation of sulfate species. The role of water vapor in flue gas might be to supplement the hydroxyl groups consumed so that the SO2 oxidation could continue.

Selective catalytic reduction of NO with NH3 over activated carbon impregnated with melamine at low temperature

Abstract N-doped activated carbons (ACM) was obtained by impregnated activated carbon (AC) with melamine (M). The relationship between the impregnated time and calcination temperature on the nitrogen content and NH3-SCR activity was investigated. Results showed that SCR activity of ACM was higher than original AC. For ACM-5-900 was about 51.67% at 80°C while AC was about 21.92%. Characterizations of BET, element analysis and XPS were employed to study the structural properties, nitrogen contents and distribution of nitrogen-containing groups of ACM. Results indicated that NO conversion of ACM was influenced by the form of nitrogen-containing functional groups rather than the nitrogen content. The NO+O2-TPD revealed that nitrogen-containing surface groups of ACM facilitated the adsorption and oxidation of NO, leading to the higher NO conversion. However, SO2 played an inhibit role on NO conversion of ACM.

In situ preparation of mesoporous Fe/TiO 2 catalyst using Pluronic F127-assisted sol-gel process for mid-temperature NH 3 selective catalytic reduction

Abstract An Fe/TiO2 catalyst with uniform mesopores was synthesized using Pluronic F127 as a structure-directing agent. This catalyst was used for selective catalytic reduction of NO with NH3. The catalytic activity and resistance to H2O and SO2 of Fe/TiO2 prepared by a template method were better than those of catalysts synthesized using impregnation and coprecipitation. The samples were characterized using N2-physisorption, transmission electron microscopy, ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, and in situ diffuse reflectance infrared Fourier-transform spectroscopy. The results showed that Pluronic F127 acted as a structural and chemical promoter; it not only promoted the formation of a uniform mesoporous structure, leading to a higher surface area, but also improved dispersion of the active phase. In addition, the larger number of Lewis acidic sites, indicated by the presence of coordinated NH3 species (1188 cm−1) and the N–H stretching modes of coordinated NH3 (3242 and 3388 cm−1), were beneficial to mid-temperature selective catalytic reduction reactions.

Selective Catalytic Reduction of NOx over Fe/TiO2 Prepared by F127- Template Method at Mid-Temperature

A series of catalysts based on Fe/TiO2 were synthesized by template, impregnation, and co-precipitation methods for mid-temperature selective catalytic reduction of NO with NH3. The samples were characterized by Brunauer-Emmett- Teller (BET), X-ray diffraction (XRD), temperature programmed desorption (TPD) and Diffuse reflectance infrared Fourier transform spectra (DRIFTS). Among these catalysts, the sample prepared by template method exhibited the best catalytic performance. Analyses indicated that large specific surface area, good dispersion of active phase, and stronger NH4+ adsorption on Bronsted acid sites might be the main reasons for the high catalytic performance of Fe/TiO2 prepared by template method.