Sodium Enhances Ir/TiO₂ Activity for Catalytic Oxidation of Formaldehyde at Ambient Temperature

Abstract

The development of highly efficient catalysts for ambient formaldehyde (HCHO) destruction is of great interest for indoor air purification. Here, we show that a sodium (Na)-doped iridium (Ir) catalyst (Ir/TiO2) is a highly active catalyst for the catalytic oxidation of HCHO at room temperature. We observed that Na addition dramatically enhanced the activity of the Ir/TiO2-R catalyst, and 100% HCHO conversion was achieved over Na-Ir/TiO2-R catalyst at a gas hourly space velocity of 100,000 h–1 and HCHO inlet concentration of 120 ppm at 25 °C. The Ir/TiO2 and Na-Ir/TiO2 catalysts were characterized using X-ray powder diffraction, Brunauer–Emmett–Teller surface area testing, high-angle annular dark-field scanning transmission electron microscopy, H2 temperature-programmed reduction (TPR), X-ray absorption fine structure, X-ray photoelectron spectroscopy, and CO-TPR. The characterization results show that the addition of Na species had no influence on Ir dispersion on the TiO2 surface but greatly promoted the activation of both chemisorbed oxygen and H2O. The reaction mechanism of HCHO oxidation was investigated by using in situ diffuse reflectance infrared transform spectroscopy. The results show that the reaction mechanisms on Ir/TiO2-R and Na-Ir/TiO2-R both followed the direct formate oxidation pathway (HCHO → HCOO + OH → CO2 + H2O), and the activated oxygen species mainly participated in the formate formation step while the activated OH groups were primarily responsible for the subsequent formate oxidation. Because of the improved capacities for the activation of oxygen and H2O induced by Na addition, the Na-Ir/TiO2 catalyst demonstrated much better performance than Ir/TiO2 for ambient HCHO oxidation.

Formaldehyde Oxidation on Pd/TiO2 Catalysts at Room Temperature: The Effects of Surface Oxygen Vacancies

“…Catalyst activity testing for HCHO oxidation was performed according to our previous work [18]. For kinetics measurement, the feed gas composition was 300 ppm HCHO at a gas hourly space velocity of 300,000 h −1 .…”

“…In comparison, catalytic oxidation is widely recognized to be the promising method because HCHO oxidation could be effectively decomposed into harmless CO 2 and H 2 O without any secondary pollution [6]. For decades, metal oxide catalysts (Ag, Mn, Co and Ni) [7][8][9][10][11][12][13][14][15][16] and supported noble metal (Pt, Au, Pd, Ir, Rh) catalysts [17][18][19][20][21] were attracting attention of researchers for HCHO oxidation. The former usually needed higher reaction temperature to completely decompose HCHO, while the later had shown excellent performance in HCHO oxidation at room temperature and thus was considered to be more suitable for indoor HCHO elimination.…”

Hydrogenated Amorphous Titania with Engineered Surface Oxygen Vacancy for Efficient Formaldehyde and Dye Removals under Visible-Light Irradiation

“…Formaldehyde, one of the most common indoor air pollutions, is highly poisonous and carcinogenic and is an immense threat to human health [ 21 , 22 ]. Photocatalytic formaldehyde purification is an efficient and safe method that can completely decompose formaldehyde into carbon dioxide and water [ 23 , 24 , 25 , 26 , 27 ]. Current studies on photocatalytic formaldehyde photodegradation are mainly focused on reaction mechanisms, such as peculiar formaldehyde physicochemical adsorption models and complex reaction pathways.…”

New Insights into Crystal Defects, Oxygen Vacancies, and Phase Transition of Ir-TiO2

“…In the recent years, the activity of Ir-doped TiO 2 (Ir-TiO 2 ) has been studied for hydrogen production, , remediation of gas pollutants, , photo-electrochemical sensing, carbon dioxide reduction, and antimicrobial activity . All these studies indicate that Ir doping is beneficial to maximize the activity of TiO 2 , through an enhanced electron–hole separation.…”