Experimental study on C<sub>3</sub>H<sub>6</sub>-SCR activity over Cu-Ni<sub><italic>x</italic></sub>-BTC catalysts

Nitrogen oxides (NO_{<italic>x</italic>}) emissions resulting from the burning of fossil fuels have detrimental effects on both human health and the environment. Therefore, it is necessary to reduce the release of NO_{<italic>x</italic>} into the atmosphere. Selective catalytic reduction of NO with C₃H₆ (C₃H₆-SCR) shows great potential because C₃H₆, as a reducing gas, not only reduces the expenses, but also offers enhanced safety and convenience, as compared to NH₃. Low-temperature denitrification process is considered to be cost-saving and energy-efficient. Improving the low-temperature denitrification activity of the catalyst is the key point and a hot topic. Cu-BTC catalyst has the advantages of an adjustable metal site, uniform pore structure and high specific surface area and shows excellent low-temperature catalytic activity in SCR of NO using NH₃ (NH₃-SCR), however, it has poor low-temperature activity when applied to C₃H₆-SCR. To overcome this limitation, in the present study, an additional metal, Ni, was introduced to Cu-BTC to enhance its low-temperature denitrification activity through intermetallic synergies effect. One-step hydrothermal technique was used to synthesize the Ni-doped Cu-Ni_{<italic>x</italic>}-BTC catalyst. The basic chemical physical properties of the catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), N₂ adsorption-desorption, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction of hydrogen (H₂-TPR) and pyridine adsorption-Fourier transform infrared spectroscopy (Py-FTIR), etc. The C₃H₆-SCR reactivity was evaluated in a fixed bed reactor with flue gas consisting 0.05% NO, 0.1% C₃H₆, 5% O₂. The results demonstrated that the introduction of Ni improved the catalytic activity of Cu-BTC. The Cu-Ni_1/2-BTC catalyst achieved a NO conversion rate of 100% and N₂ selectivity of 98.3% at 250−275 ℃, and the C₃H₆ conversion rate of Cu-Ni_1/2-BTC is higher at the same temperature, and the C₃H₆ conversion temperature moves to low temperature. The resistance to SO₂ of Cu-Ni_1/2-BTC catalyst was tested. Results showed, when there was 0.02% SO₂ in the simulated flue gas, the NO conversion rate of Cu-Ni_1/2-BTC decreased to 89.2% at 275 ℃ because of the formation of sulfate on the catalyst surface. Characterization results demonstrated that Ni was effectively doped into the catalyst framework structure and evenly distributed over the catalyst surface. Results from XRD patterns and SEM images demonstrated that Cu-Ni_{<italic>x</italic>}-BTC retained the characteristics peaks and basic morphology of Cu-BTC. The XPS spectra showed that the doped Ni existed as Ni²⁺ and Ni³⁺, and that once Ni was doped, the Cu⁺ content in the catalysts increased, suggesting that there was strong electron transfer between Ni and Cu. As the Ni content increased, the specific surface area and pore volume of the catalysts progressively decreased, while the pore size initially increased and then decreased. The H₂-TPR data proved that when Ni was doped, the reduction peaks of the catalysts shifted to a lower temperature and exhibited a higher reduction capacity. Results showed that Cu-Ni_{<italic>x</italic>}-BTC possessed better redox properties at low temperatures, more surface-adsorbed oxygen, more Cu⁺ ions, and more Lewis acid than Cu-BTC, all of which contributed to its increased catalytic activity.