Unlocking the Potential of Metal-Doping Fe2O3/Rice Husk Ash Catalysts for Low-Temperature CO-SCR Enhancement

Transition metal oxides are efficient bifunctional catalysts for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) using CO. Nonetheless, their poor activity at lower temperatures constrains broader industrial application. Herein, we propose an optimized Fe2O3-based catalyst through strategic metal doping with Cu, Co, or Ce, which engenders a harmonious balance for the synergistic removal of CO and NOx. Among the developed catalysts, Co-doped Fe2O3, supported by rice husk ash, demonstrates superior low-temperature CO-SCR activity, achieving CO and NOx conversion ratios and N2 selectivity above 98.5% at 100-500 °C. The enhanced catalytic performance is attributed to the catalyst's improved redox properties and acidity, engendered by strong Fe-Ox-Co interactions. Furthermore, the CO-SCR reaction adheres to the Langmuir-Hinshelwood and Eley-Rideal mechanisms. Our findings shed light on the future industrial application of low-temperature CO and NOx near-zero emission technology and provide a strategy for the design of low-cost SCR catalysts.

Enhanced activity and sulfur resistance of Cu- and Fe-modified activated carbon for the reduction of NO by CO from regeneration gas

The reduction of NO by CO was proposed to be applied for regeneration gas to remove NOx from industrial flue gas with activated carbon purification technology.

A review of the catalysts used in the reduction of NO by CO for gas purification

The reduction of NO by the CO produced by incomplete combustion in the flue gas can remove CO and NO simultaneously and economically. However, there are some problems and challenges in the industrial application which limit the application of this process. In this work, noble metal catalysts and transition metal catalysts used in the reduction of NO by CO in recent years are systematically reviewed, emphasizing the research progress on Ir-based catalysts and Cu-based catalysts with prospective applications. The effects of catalyst support, additives, pretreatment methods, and physicochemical properties of catalysts on catalytic activity are summarized. In addition, the effects of atmosphere conditions on the catalytic activity are discussed. Several kinds of reaction mechanisms are proposed for noble metal catalysts and transition metal catalysts. Ir-based catalysts have an excellent activity for NO reduction by CO in the presence of O₂. Cu-based bimetallic catalysts show better catalytic performance in the absence of O₂, in that the adsorption and dissociation of NO can occur on both oxygen vacancies and metal sites. Finally, the potential problems existing in the application of the reduction of NO by CO in industrial flue gas are analyzed and some promising solutions are put forward through this review.

Study of a catalyst supported on rice husk ash for NO reduction with carbon monoxide

Fe–Cu catalysts supported on rice husk ash were used in CO-SCR of NO and this new combination was effective.

Kinetics, Isotherms and Thermodynamic Modeling of Liquid Phase Adsorption of Crystal Violet Dye onto Shrimp-Waste in Its Raw, Pyrolyzed Material and Activated Charcoals

Shrimp waste and its charcoal derivatives were evaluated for the removal of crystal violet. Activation was conducted at 500 °C with phosphoric acid at the 1:2 and 1:3 ratios. Activated charcoals were more porous and had a more roughly surface containing mainly C, O, Ca N, and P. Equilibrium adsorption data were fitted using seven kinetic and six isotherms models. Activation created acidic moieties (>4700 µmol/g) and reduced the point of zero charge (<2.5). Freundlich isotherm best described the uptake of the dye onto the adsorbents suggesting a heterogeneous adsorption, whereas the Bangham and Avrami models best described the kinetics of adsorption process. An endothermic and spontaneous physisorption was responsible for the sorption phenomena in most adsorbents. The high removal of crystal violet was attributed to the high ionization capacity of the adsorbent coupled with the high external surface area (>44 m2/g). The best adsorption capacity (208 mg/g) was found for the activated and charred materials, whereas the lowest one (3.9 mg/g) was found for the pyrolyzed material. This research creates the possibility to deal with two environmental problems: (i) the reuse of shrimp waste and (ii) the removal of water pollutants such as crystal violet.

Investigation of low-temperature selective catalytic reduction of NOx with ammonia over Cr-promoted Fe/AC catalysts

Fe/activated coke (AC) and Cr-Fe/AC catalysts with AC as a supporter and Cr and Fe as active components were prepared by an impregnation method for low-temperature selective catalytic reduction (SCR) of NO with NH₃. The effects of Cr addition and its concentrations on the deNO_x performance of Fe/AC catalysts were studied at low temperature. The Cr addition promotes the low-temperature SCR activity of the 8Fe/AC catalyst and the 8Fe6Cr/AC catalyst has the best low-temperature SCR deNO_x performance, which the NO_x conversions are greater than 90% at 160-240 °C. The 8Fe6Cr/AC catalyst has good water resistance. However, when 100 ppm SO₂ was introduced into the reaction gas, its deNO_x efficiency drops to 45% at 180 °C. To clarify the specific effects of Cr addition on the NO_x conversions and sulfur poisoning, the Cr-Fe/AC catalysts were characterized by X-ray diffraction, BET, H₂ temperature-programmed reduction, NH₃ temperature-programmed desorption, X-ray photoelectron spectroscopy, and Fourier infrared spectroscopy. The addition of Cr into Fe/AC catalysts greatly increases the BET surface area and the number of weak and medium-strong acid sites on the catalyst surface and improves the ratio of Fe³⁺/Fe²⁺. These factors enhance the NO_x conversion of 8Fe/AC catalyst. The formed sulfates and hydrogen sulfates cover the active sites on the catalyst surface, which lead to the sulfur poisoning of the 8Fe6Cr/AC catalyst. Graphical abstract.

N-Doped FeCo/ASC catalysts for NOx reduction by CO in a simulated rotary reactor

Herein, nitrogen-doped activated semi-coke (ASC)-supported ferrum cobalt-co-impregnated catalysts (FeCo/N-ASC) were prepared and tested for deNO_x in a simulated rotary reactor.

NO x reduction by CO over ASC catalysts in a simulated rotary reactor: effect of CO2, H2O and SO2

The influence of CO₂, H₂O and SO₂ on the NO reduction by CO over Fe/Co activated semi-coke catalyst was investigated in a simulated rotary reactor. The results showed that, in the simulated rotary reactor, the influence of CO₂ and H₂O on the NO adsorption was significant at low temperatures, and the inhibition became weak when increasing the temperature. However, the NO adsorption efficiency could not be improved by increasing temperature after catalyst sulfur poisoning. The heavily inhibited NO adsorption process, which was due to the competitive adsorption and formation of the sulfate, resulted in a low NO reduction efficiency in the presence of CO₂, H₂O or SO₂. The in situ DRIFT study showed that the dominant effect of CO₂, H₂O and SO₂ on the NO adsorption was the inhibition of the free nitrate ions formation. In addition, the introduction of CO₂, H₂O and SO₂ could not change the route of NO reduction, but just reduced the degree of the NO + CO reduction.

The influence of CO₂, H₂O and SO₂ on the NO reduction by CO over Fe/Co activated semi-coke catalyst was investigated in a simulated rotary reactor.

Investigation of SO2tolerance of Ce-modified activated semi-coke based catalysts for the NO + CO reaction

The SO₂tolerance mechanism of Ce-modified activated semi-coke based catalysts for the NO + CO reaction.