Accelerated industrialization and population growth have led to a rapid surge in the demand for fossil fuels. Being a large environmental pollutant, various stringent measures have been enacted to minimize and possibly eliminate the use of fossil fuels. These regulations measures aim to achieve certain emissions targets which require urgent and aggressive methods to realize. These are not limited to renewable technology, clean and efficient emission technologies.
In particular, nitrogen oxides removal has undergone incredible evolution from traditional methods to current advanced and more efficient methods. The selective catalytic reduction of nitrogen oxides with hydrocarbon (HC-SCR) has been very instrumental. It has paved the way for the development of porous clay heterostructures (PCHs) modified with transitional metals for enhanced catalytic activities. Past reviews have even further shown that development of catalysts for the desired reaction will further enhance selective catalytic reduction of nitrogen oxides at low temperatures. The underlying challenges can be overcome by utilizing copper and iron spinel oxides.
Recently, Minhao Yuan (Ph.D. Student), Professor Yaxin Su, and Professor Wenyi Deng from Donghua University together with Professor Hao Zhou from Changzhou Institute of Engineering Technology investigated the SCR of NO with propylene over porous clay heterostructures modified with CuFe2O4. Various catalyst characterization methods such as X-ray diffraction were used to analyze the influence of the catalytic activities at different temperatures. The main objective was to determine a reasonable and effective reaction path for the selective catalytic reduction process. Their research work is published in the Chemical Engineering Journal.
Results show that the selective catalytic reduction activities of the catalysts were highly enhanced by the formation of the CuFe2O4 species. At low temperatures, high SCR activity was observed in CuFe-PCH. This was because, at higher temperatures, the combustion reaction between oxygen and propylene was dominant thus decreasing the NO conversion. Among the tested catalysts, Cu1Fe-PCH catalyst with an equal molar ration of iron and copper recorded the highest NO removal efficiency of 58.5% at 300 °C that increased to almost 100% at 350 °C when the concentration of propylene was increased from 0.1% to 0.3%.
Based on image observations from the catalytic characterization methods, CuFe2O4 nanocrystal with two planes was observed to be the most active component of the CuFe-PCH catalyst. On the other hand, the high catalyst performance of CuFe2O4 species on CuFe-PCH catalyst was also attributed to its enhanced properties: high acidic site density, high crystallinity, large lattice oxygen proportionality, good redox ability among others. The increase in the copper content resulted in a decrease in the pore volume and surface area due to partial blockage of the porous clay heterostructure channels.
From the Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS) results, a possible reaction path of selective catalytic reduction of nitrogen oxide was proposed. This was mainly due to the formation of more isocyanates such as Cu-NCO and Fe-NCO that greatly contributed to improving the C3H6-SCR activity. When these intermediates were reacted with adsorbed nitrogen oxide species, water, nitrogen and carbon dioxide were formed. Overall, the results suggest that the presented porous clay heterostructures modified with copper ferrite spinel catalysts is promising in curbing environmental pollution through efficient selective catalytic reduction of nitrogen oxides.
Yuan, M., Su, Y., Deng, W., & Zhou, H. (2019). Porous clay heterostructures (PCHs) modified with copper ferrite spinel as catalyst for SCR of NO with C3H6. Chemical Engineering Journal, 375, 122091.