Formulating the Li sites of Li-CoOx composites for achieving high-efficiency oxidation removal of formaldehyde over the Ag/Li-CoOx catalyst under ambient conditions

Oxide supported noble metals are extensively investigated for ambient formaldehyde oxidation, and the Ag-CoOx complex is one promising combination in terms of cost and activity. Further, we previously observed that cooperating Ag with Li+ greatly boosted formaldehyde degradation on CoOx. Yet, there is still room for improvement in removal efficiency, mineralization capacity and resistance to severe conditions. These objectives could be realized via strategically formulating the Li+ sites of Li-CoOx composite in this sister study. Three samples with Li (+) -Co3+-O2- connections (L-CO), spinel Li+ (LCO-S) and layered Li+ (LCO-L) were obtained at low (300 degrees C), moderate (500 degrees C) and high (700 degrees C) temperatures, respectively. The specific Li+ positions and componential interaction were demonstrated by Hyperspectral imaging (HSI), XRD, SEM, TEM, HAADF mapping, UV-vis DRS and XPS. Moreover, the effect of reactive oxygen exposure on catalytic oxidation of formaldehyde (330-350 mg/m3) was disclosed through CO-TPR and O-2-TPD. Compared with the LCO-S and LCO-L, LCO exhibited dominant formaldehyde degradation due to the larger content of surface oxygen. After Ag decoration, the Li+-Co3+-O2- connections uniquely caused a strong binding of Ag species with catalyst host, which boosted the amount of reactive oxygen and finally resulted in an even higher elimination of similar to 73% (CO2 yield = similar to 21%), 47% higher than that of the L-CO (CO2 yield = similar to 6%). But in contrast, the Ag@LCO-S only achieved similar to 53% removal (CO2 yield = similar to 9%) and Ag modification was powerless in altering the inertness of LCO-L, demonstrating that the chemical environment of alkali metal is crucial to effectively tuning the catalyst activity. The advantage of Ag@L-CO in formaldehyde depollution was further reflected from its much better resistance to moisture and aromatic compound omnipresent in indoor air. For the first time, this study extended the understanding of the alkali-metal-promoted formaldehyde oxidation reaction to an in-depth level.

Automated summary

In this study, three samples were prepared by strategically formulating the Li+ sites of Li-CoOx composite, and their structures and componential interactions were characterized by various techniques. After Ag decoration, the Li+-Co3+-O2- connections uniquely caused a strong binding of Ag species with catalyst host, resulting in an increased amount of reactive oxygen and improved formaldehyde degradation efficiency and mineralization capacity. Additionally, Ag@L-CO exhibited better resistance to moisture and aromatic compounds omnipresent in indoor air compared to other samples.