Investigation into Photocatalytic Degradation of Gaseous Ammonia in CPCR

Enhanced photocatalytic ammonia oxidation activity and nitrogen selectivity over Ag/AgCl/N-TiO2 photocatalyst

The removal of ammonia (NH3) emitted from agricultural and industrial activities is of great significance to protect human health and ecological environment. Photocatalytic NH3 oxidation to N2 under mild conditions is a promising strategy. However, developing visible light photocatalysts for NH3 oxidation is still in its infancy. Here, we fabricate N-TiO2 and Ag/AgCl/N-TiO2 photocatalysts by sol-gel and photodeposition methods, respectively. The introduction of N not only endows TiO2 with visible light response (absorption edge at 460 nm) but also results in the formation of heterophase junction (anatase and rutile). Thus, N-TiO2 shows 2.0 and 1.8 times higher than those over anatase TiO2 and commercial TiO2 for NH3 oxidation under full spectrum irradiation. Meanwhile, surface modification of Ag can simultaneously enhance visible light absorption (generating localized surface plasmon resonance effect) and charge separation efficiency. Therefore, the photocatalytic activity of Ag/AgCl/N-TiO2 is further improved. Furthermore, the presence of N and Ag also enhances the selectivity of N2 product owing to the change of reaction pathway. This work simultaneously regulates photocatalytic conversion efficiency and product selectivity, providing some guidance for developing highly efficient photocatalysts for NH3 elimination.

Comprehensive evaluation of an ionic liquid based deep purification process for NH3-containing industrial gas

Ammonia (NH3) emission has caused serious environment issues and aroused worldwide concern. The emerging ionic liquid (IL) provides a greener way to efficiently capture NH3. This paper provides rigorous process simulation, optimization and assessment for a novel NH3 deep purification process using IL. The process was designed and investigated by simulation and optimization using ionic liquid [C4im][NTF2] as absorbent. Three objective functions, total purification cost (TPC), total process CO2 emission (TPCOE) and thermal efficiency (ηeff) were employed to optimize the absorption process. Process simulation and optimization results indicate that at same purification standard and recovery rate, the novel process can achieve lower cost and CO2 emission compared to benchmark process. After process optimization, the optimal functions can achieve 0.02726 $/Nm3 (TPC), 311.27 kg CO2/hr (TPCOE), and 52.21% (ηeff) for enhanced process. Moreover, compared with conventional process, novel process could decrease over $ 3 million of purification cost and 10000 tons of CO2 emission during the life cycle. The results provide a novel strategy and guidance for deep purification of NH3 capture.

A figure of merits-based performance comparison of various advanced functional nanomaterials for adsorptive removal of gaseous ammonia

The implementation of sustainable industrial development based on energy/cost-effective techniques with zero/low rate of pollutant emission is an ideal strategy for the proper management of a natural environment. Gaseous ammonia released from a variety of anthropogenic sources (e.g., agriculture, pharmaceuticals, commercial cleaning products, and refrigerant) is estimated to be as high as 150 million tons∙year^-1. To reduce the negative effects of atmospheric ammonia, the great utility of advanced functional nanomaterials (e.g., metal organic frameworks, covalent organic polymers, metal/metal oxide nanoparticles, and carbon nanostructures) has been recognized. To gain a better understanding of the sorptive removal potential of diverse materials, their performance has been evaluated based on the key performance merits (e.g., initial concentration, sorption capacity, and partition coefficient). Generally, the PC values can be applied to significantly estimate the contaminant adsorption potential of NMs via balancing the biased influences of operating parameters (e.g., initial concentration of pollutants) as perceived for the partitioning of compounds between aqueous phases at equilibrium (e.g., Henry's Law). Therefore, in this work, we have proposed the PC as a prosperous performance merit (in terms of heterogeneity of surface and strength of adsorption process) for the selection of high performance nano-adsorbents for gaseous ammonia. Moreover, the water stability, recyclability, economic aspects, and future perspectives have also been discussed for real-world applications of advanced nanomaterial against gaseous ammonia adsorption. The outcome of this evaluation will be expedient for the classification/selection of the most effectual and cost-effective options for mitigation of environmental pollutants like gaseous ammonia.

Photocatalytic reaction mechanisms at the gas–solid interface for environmental and energy applications

Five gas–solid photocatalytic reactions including the oxidation of NOx, VOCs and NH3, and reduction of CO2 and N2 are summarized. Besides, basic properties of gas molecules, their adsorption and activation, and various reaction pathways are analyzed.

Effect of TiO2 calcination temperature on the photocatalytic oxidation of gaseous NH3

Carbon-modified titanium dioxide (TiO2) was prepared by a sol-gel method using tetrabutyl titanate as precursor, with calcination at various temperatures, and tested for the photocatalytic oxidation (PCO) of gaseous NH3 under visible and UV light. The test results showed that no samples had visible light activity, while the TiO2 calcined at 400°C had the best UV light activity among the series of catalysts, and was even much better than the commercial catalyst P25. The catalysts were then characterized by X-ray diffractometry, Brunauer-Emmett-Teller adsorption analysis, Raman spectroscopy, thermogravimetry/differential scanning calorimetry coupled with mass spectrometry, ultraviolet-visible diffuse reflectance spectra, photoluminescence spectroscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy. It was shown that the carbon species residuals on the catalyst surfaces induced the visible light adsorption of the samples calcined in the low temperature range (< 300°C). However, the surface acid sites played a determining role in the PCO of NH3 under visible and UV light over the series of catalysts. Although the samples calcined at low temperatures had very high SSA, good crystallinity, strong visible light absorption and also low PL emission intensity, they showed very low PCO activity due to their very low number of acid sites for NH3 adsorption and activation. The TiO2 sample calcined at 400°C contained the highest number of acid sites among the series of catalysts, therefore showing the highest performance for the PCO of NH3 under UV light.

Production of copper-based rare earth composite metal materials by coprecipitation and applications for gaseous ammonia removal

This study addresses the oxidation of ammonia (NH3) at temperatures between 423 and 673 K by selective catalytic oxidation (SCO) over a copper-based, rare earth composite metal material that was prepared by coprecipitating copper nitrate, lanthanum nitrate, and cerium nitrate at various molar ratios. The catalysts were characterized using Brunner, Emmett, and Teller spectroscopy, Fourier-transform infrared spectroscopy, Xray diffraction, ultraviolet-visible spectroscopy, cyclic voltammetric spectroscopy, and scanning electron microscopy. At a temperature of 673 K and an oxygen content of 4%, approximately 99.5% of the NH3 was reduced by catalytic oxidation over the 6:1:3 copper-lanthanum-cerium (molar ratio) catalyst. Nitrogen (N2) was the main product of this NH3-SCO process. Results from the activity and selectivity tests revealed that the optimal catalyst for catalytic performance had the highest possible cerium content and specific surface area (43 m2/g).