Alkali‐Metal‐Promoted Pt/TiO₂ Opens a More Efficient Pathway to Formaldehyde Oxidation at Ambient Temperatures

Abstract

Formaldehyde is emitted from building and furnishing materials and consumer products, [1] and is known to cause irritation of eyes and respiratory tract, headache, pneumonia, and even cancer. [2,3] It is a dominant indoor air pollutant, especially in developing countries, and significant efforts have gone into indoor HCHO purification to meet environmental regulations and human health needs.Removal of HCHO by adsorbents has been investigated extensively using potassium permanganate, activated carbon, aluminum oxide, and some ceramic materials. [4][5][6] Sorbent effectiveness is typically limited by low adsorption capacities. Catalytic oxidation is the most effective technology for volatile organic compound (VOC) abatement because VOCs can be oxidized to CO 2 over certain catalysts at much lower temperatures than in thermal oxidation. [7][8][9] Supported noble metal catalysts (Pt, Pd, Rh, Au, Ag) or metal oxide catalysts (Ni, Cu, Cr, Mn) have been used for the catalytic oxidation of VOCs. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Complete oxidation of HCHO over catalysts occurs above 150 8C on clean and oxidized films of Ni, Pd, and Al [15] and over silver-cerium composite oxide, [16] above 100 8C over Ag/MnOx-CeO 2 [18] and Au/CeO 2 , [19] and above 85 8C over Pd-Mn/Al 2 O 3[17] and Au/FeOx. [20] As catalytic oxidation at even lower temperatures is desirable for indoor air purification, the development of a catalyst for total HCHO oxidation at room temperature is of great interest. In our recent study, [21,22] 1 % Pt/TiO 2 catalyst was shown to be effective for HCHO oxidation at room temperature, achieving 100 % conversion of d = 100 ppm HCHO to CO 2 and H 2 O at a gas hourly space velocity (GHSV) of 50 000 h À1 . However, we also observed that this type catalyst is not as active as needed for practical applications, and deactivates with time-on-stream.Herein, we report a novel alkali-metal-promoted Pt/TiO 2 catalyst for the ambient destruction of HCHO. We show that the addition of alkali-metal ions (such as Li + , Na + , and K + ) to Pt/TiO 2 catalyst stabilized an atomically dispersed Pt-O(OH)x-alkali-metal species on the catalyst surface and also opened a new low-temperature reaction pathway, significantly promoting the activity for the HCHO oxidation by activating H 2 O and catalyzing the facile reaction between surface OH and formate species to total oxidation products.Figure 1 a shows the HCHO conversion to CO 2 as a function of temperature over the x % Na-1 % Pt/TiO 2 (x = 0, 1, and 2) samples at a GHSV of 120 000 h À1 and HCHO inlet of d = 600 ppm. All gas streams were humidified to a RH of around 50 %. Before each activity test, the samples were reduced in H 2 at 300 8C for 30 min. The sodium-free catalyst had low activity for the HCHO oxidation reaction, with HCHO conversion being only about 19 % at 15 8C. With 1 % Na addition, the HCHO conversion reached 96 % at 15 8C and 100 % at 40 8C. With 2 % Na addition, 100 % HCHO conversion to CO 2 and H 2 O was measured at 15 8C. The effect of ...

Single-Atom Catalysts: A New Frontier in Heterogeneous Catalysis

“…In this case, the anchoring sites with surface species of the support as ligands, such as surface uncapped sites or other aggregation inhibitors on supports like alkali-ion contaminants or residual organic ligands during chemical preparations, will play an essential role in stabilizing single-atom metal species. 18,24,25,38,39 Inasmuch as the anchoring sites on the support are not always abundant, low loadings of metal with high-surface-area supports are generally required to achieve SACs. 18,24,26,31 2.2.…”

Catalytic oxidation of formaldehyde over manganese oxides with different crystal structures

“…Several approaches for HCHO removal have been studied during decades of research, including photo-catalytic oxidation, 5,6 plasma decomposition with catalyst, 7 adsorption 8 and catalytic oxidation. [9][10][11] However, photo-catalytic oxidation needs light containing ultraviolet wavelengths to excite the catalyst, and may lead to the formation of harmful by-products. Plasma technology has significant limitations such as the poor performance under low concentrations of HCHO and possible harmful by-products such as ozone.…”

Influence of alkali metals on Pd/TiO2catalysts for catalytic oxidation of formaldehyde at room temperature

“…[4][5][6][7][8][9] Among these methods, catalytic oxidation is known as the most promising method for HCHO removal, which could selectively decompose HCHO to harmless CO 2 and water at a low temperature without any secondary pollution. 10,11 For decades, researchers paid attention to conventional catalysts including metal oxides (Co, Ni, Mn, Ag) 3,[12][13][14][15][16][17][18][19][20] and supported noble metal (Pt, Au, Pd, Rh) catalysts [21][22][23][24][25][26][27][28][29][30][31][32][33] for HCHO oxidation. A relatively high temperature is generally needed to completely oxidize HCHO using the metal oxide catalysts.…”

“…In contrast, complete oxidation of HCHO can achieved on noble metal catalysts, such as Pt-, Au-and Pd-based catalysts, around room temperature. [21][22][23][24]27,31 Therefore, the supported noble metal catalysts are more suitable for indoor air HCHO purification. Alkali metals can serve as electronic or textural promoters for catalysts in various catalytic processes 34 including NO 35 and CO oxidation, 36,37 CO hydrogenation 38 and the water-gas shift reaction.…”