Fujiao Song

Adsorption of carbon dioxide on amine-modified TiO2 nanotubes.

TiO2 nanotubes (TiNT) were prepared by a hydrothermal treatment and modified by three kinds of amines, namely ethylenediamine, polyetherimide and tetraethylenepentamine (TEPA), to study their CO2 adsorption properties from gas streams. The resultant samples were characterized by X-ray diffraction, transmission electron microscopy, and infrared spectroscopy, as well as low temperature N2 adsorption. CO2 capture was investigated in a dynamic packed column at 30 degrees C. TEPA-modified TiO2 nanotubes showed the highest adsorption capacity of 167.64 mg/g because it had the highest amino-group content among the three amines. CO2 fixation on TiNT impregnated by TEPA was investigated at 30, 50, and 70 degrees C, and the adsorption capacity increased slightly with temperature. Following the adsorption step, the sorbents were regenerated by temperature programmed desorption, and the TiNT-TEPA sample, as CO2 sorbent, was found to be readily regenerated and energy-efficient. The cycle test also revealed that the TiNT-TEPA adsorbent is fairly stable, with only a 5% drop in the adsorption capacity after 10 adsorption/desorption cycles. In addition, the CO2 adsorption behavior was investigated with the deactivation model, and which showed an excellent prediction for the TiNT-TEPA breakthrough curves.

Capture of carbon dioxide from flue gas on TEPA-grafted metal-organic framework Mg2(dobdc).

Carbon dioxide (CO2) adsorption on a standard metal-organic framework Mg2(dobdc) (Mg/DOBDC or Mg-MOF-74) and a tetraethylenepentamine (TEPA) modified Mg2(dobdc) (TEPA-Mg/DOBDC) were investigated and compared. The structural information, surface chemistry and thermal behavior of the adsorbent samples were characterized by X-ray powder diffraction (XRD), infrared spectroscopy (IR), thermogravimetric analysis (TGA) and nitrogen adsorption-desorption isotherm analysis. CO2 adsorption capacity was measured by dynamic adsorption experiments with N2-CO2 mixed gases at 60 degrees C. Results showed that the CO2 adsorption capacity of Mg/DOBDC was significantly improved after amine modification, with an increase from 2.67 to 6.06 mmol CO2/g adsorbent. Moreover, CO2 adsorption on the TEPA-Mg/DOBDC adsorbent was promoted by water vapor, and the adsorption capacity was enhanced to 8.31 mmol CO2/g absorbent. The adsorption capacity of the TEPA-Mg/DOBDC adsorbent dropped only 3% after 5 consecutive adsorption/desorption cycles. Therefore, this kind of adsorbent can be considered as a promising material for the capture of CO2 from flue gas.

Alkali metal cation doping of metal-organic framework for enhancing carbon dioxide adsorption capacity

Abstract Metal-organic frameworks (MOFs) have attracted much attention as adsorbents for the separation of CO 2 from flue gas or natural gas. Here, a typical metal-organic framework HKUST-1(also named Cu-BTC or MOF-199) was chemically reduced by doping it with alkali metals (Li, Na and K) and they were further used to investigate their CO 2 adsorption capacities. The structural information, surface chemistry and thermal behavior of the prepared adsorbent samples were characterized by X-ray powder diffraction (XRD), thermo-gravimetric analysis (TGA) and nitrogen adsorption-desorption isotherm analysis. The results showed that the CO 2 storage capacity of HKUST-1 doped with moderate quantities of Li + , Na + and K + , individually, was greater than that of unmodified HKUST-1. The highest CO 2 adsorption uptake of 8.64 mmol/g was obtained with 1K-HKUST-1, and it was ca. 11% increase in adsorption capacity at 298 K and 18 bar as compared with HKUST-1. Moreover, adsorption tests showed that HKUST-1 and 1K-HKUST-1 displayed much higher adsorption capacities of CO 2 than those of N 2 . Finally, the adsorption/desorption cycle experiment revealed that the adsorption performance of 1K-HKUST-1 was fairly stable, without obvious deterioration in the adsorption capacity of CO 2 after 10 cycles.

Mesoporous TiO2 as the support of tetraethylenepentamine for CO2 capture from simulated flue gas

Mesoporous TiO2 (MT) was prepared by a hydrothermal method and used as the supporting material for the immobilization of tetraethylenepentamine (TEPA) to develop a new type of adsorbent for CO2 capture from flue gas. The CO2 adsorption capacity increases with the increase of the TEPA loading amounts. With the maximum TEPA loading of 31 wt% onto the MT sorbent, the maximum CO2 adsorption capacity reached 2.52 mmol of CO2 g−1 of sorbent. In the presence of an appropriate amount of water vapor, the formation of bicarbonate and hydroxylated surface on TiO2 can improve CO2 adsorption capacity from 2.64 to 2.91 mmol g−1. However, an excess of water vapor leads to a decrease in the CO2 adsorption capacity from 2.91 to 2.65 mmol g−1, probably attributed to the adsorption competition between water and CO2. The absorption/regeneration cycle was repeated and the CO2 adsorption capacity decreased from 2.52 to 2.41 mmol g−1 over 5 cycles, almost completely maintained its original CO2 adsorption capacity. In addition, the effect of long-term storage on CO2 adsorption capacity is studied. After approximately one year of storage, the CO2 capacity of the MT–TEPA-31 decreased by 28% compared with the fresh sample.

Capture of carbon dioxide by amine-loaded as-synthesized TiO2 nanotubes

Titanium-based adsorbents for CO2 capture were prepared through impregnating the as-synthesized TiO2 nanotubes (TiNT) with four kinds of amines, namely monoethanolamine (MEA), ethylenediamine (EDA), triethylenetetramine (TETA) and tetraethylenepentamine (TEPA). The resultant samples were characterized by X-ray diffraction, low-temperature N2 adsorption as well as transmission electron microscopy. The absorption of CO2 was carried out in a dynamic packed column. The sample impregnated with TEPA showed a better adsorption capacity due to its higher amino groups content. In addition, CO2 adsorption capacity increases as the amount of amine loaded increases. Therefore, TiNT-TEPA-69 showed the highest CO2 adsorption capacity among the three samples impregnated with TETA; approximately 4.10 mmol/g at 30°C. In addition, the dynamic adsorption/desorption performance was investigated. The adsorption capacity of TiNT-TEPA-69 dropped slightly (about 2%) during a total of five cycles. The TiNT-TEPA-69 adsorbent exhibited excellent CO2 adsorption/desorption performance.

Promotional effect and mechanism study of nonmetal-doped Cr/CexTi1−xO2 for NO oxidation: tuning O2 activation and NO adsorption simultaneously

Nonmetal-doped Cr/CexTi1−xO2 catalysts were evaluated for selective catalytic oxidation (SCO) of NO, and these were synthesized by using cyanamide as a nonmetal source. The aim of this paper was to elucidate the detailed composition–structure–property relationships. The characterization results demonstrated that the optimized performance was correlated with the formation of superoxide radicals, which was derived from the nonmetal doping and confirmed by EPR studies. H2-TPR and O2-TPD experiments indicated that the addition of cyanamide was beneficial to tune O2 activation and improve NO adsorption strength simultaneously. XPS results suggested that N species were successfully incorporated into the lattice of a cerium–titanium solid solution and substituted for oxygen. Additionally, the designed FTIR and Raman measurements were applied to identify the doping sites, that is, N species were inclined to substitute the O atoms around cerium to form the Ce–N–Ti and Ce–N–Ce bonds. Finally, the catalytic mechanism was tentatively proposed based on the analysis of in situ DRIFTS results.

Enhanced catalytic ozonation over reduced spinel CoMn2O4 for NOx removal: active site and mechanism analysis

In this paper, CO atmosphere reduced cobalt manganate (CoMn2O4/CO), prepared by a hydrothermal method, was successfully utilized in catalytic ozonation for NOx removal. CoMn2O4/CO shows higher activity (84%) than CoMn2O4/air (82%), Co3O4 (76%) and Mn2O3 (76%). Hydroxyl radicals (·OH) have been detected in the catalytic ozonation process, which has been confirmed to determine the catalytic performance of NOx removal. Compared to Co3O4 and Mn2O3, CoMn2O4 exhibits more surface hydroxyl groups and oxygen vacancies, both of which are critical for the ·OH generation. More importantly, more oxygen vacancies are generated when the CoMn2O4 is calcined in the reduced atmosphere. These oxygen vacancies benefit the adsorption of sufficient H2O to yield active surface –OH on the catalyst surface, promoting the adsorption of O3 on the surface –OH and thus the production of ·OH radicals. A possible mechanism for the catalytic ozonation of NOx was proposed.

Low-Temperature NOX (x = 1, 2) Removal with •OH Radicals from Catalytic Ozonation over α-FeOOH

ABSTRACT FeOOH(H), FeOOH(P) and FeOOH(O) prepared by hydrothermal, precipitant-hydrolysis and oxidation-hydrolysis methods were tested as ozonation catalysts for the low-temperature NOX (x = 1, 2) removal. FeOOH(H) exhibits higher catalytic activities than FeOOH(P) and FeOOH(O), achieving 85.6% of NOX removal efficiency with a low ozone concentration. Compared to FeOOH(P) and FeOOH(O), FeOOH(H) shows much higher BET surface areas and higher density of surface -OH, both of which are critical for the •OH radical generation over the catalysts. These radicals can be successfully transferred into the duct under the coupling effect of hydroxyl radicals and O3, oxidizing and removing the NOX (x = 1, 2). Results of ion chromatography (IC) indicate that the oxidation products are all NO3− without any NO2− in the tail solutions.

UiO-66-NH2/GO Composite: Synthesis, Characterization and CO2 Adsorption Performance

In this work, a new composite materials of graphene oxide (GO)-incorporated metal-organic framework (MOF)(UiO-66-NH2/GO) were in-situ synthesized, and were found to exhibit enhanced high performances for CO2 capture. X-ray diffraction (XRD), scanning electron microscope (SEM), N2 physical adsorption, and thermogravimetric analysis (TGA) were applied to investigate the crystalline structure, pore structure, thermal stability, and the exterior morphology of the composite. We aimed to investigate the influence of the introduction of GO on the stability of the crystal skeleton and pore structure. Water, acid, and alkali resistances were tested for physical and chemical properties of the new composites. CO2 adsorption isotherms of UiO-66, UiO-66-NH2, UiO-66/GO, and UiO-66-NH2/GO were measured at 273 K, 298 K, and 318 K. The composite UiO-66-NH2/GO exhibited better optimized CO2 uptake of 6.41 mmol/g at 273 K, which was 5.1% higher than that of UiO-66/GO (6.10 mmol/g). CO2 adsorption heat and CO2/N2 selectivity were then calculated to further evaluate the CO2 adsorption performance. The results indicated that UiO-66-NH2/GO composites have a potential application in CO2 capture technologies to alleviate the increase in temperature of the earth’s atmosphere.

In Situ Fabrication of 3D Octahedral g-C3N4/BiFeWO x Double-Heterojunction for Highly Selective CO2 Photoreduction to CO Under Visible Light

A series of g‐C3N4/BiFeWOx composites (GN‐x/BFW) with double‐heterojunction composites as photocatalysts for efficient and stable CO2 photoreduction had been rationally designed and synthesized by the facile in situ hydrothermal method. In situ growing BFW on g‐C3N4 sheets achieved that the g‐C3N4 was embedded in the inner of BFW as well as wrapped on the surfaces of BFW. The obtained heterojunction composites greatly inhibited the recommendation of photogenerated electron/hole pairs and enhanced the light respond on the visible light due to the tight chemically bonded interface interaction. Benefiting from the unique structure, the optimized GN‐5.0 %/BFW heterostructure catalyst showed a higher performance of photoreduction CO2 to CO (43 μmol h−1 g−1) than that of pure BFW (5.2 μmol h−1 g−1) and g‐C3N4 (8.9 μmol h−1 g−1) under visible light irradiation at 10 °C. Besides, the GN‐x/BFW composites exhibited outstanding recycling photostability and structural stability. A possible Z‐scheme mechanism was proposed according to the staggered band potentials between g‐C3N4 and BFW and ESR results. Similarly, this facile synthetic method could be employed to fabricate other composites to accelerate the photocatalytic performance.