A TiO2/C catalyst having biomimetic channels and extremely low Pt loading for formaldehyde oxidation

Abstract

This study presents a TiO₂/C hybrid material with biomimetic channels fabricated using a wood template. Repeated impregnations of pretreated wood chips in a Ti precursor were conducted, followed by calcination at 400-600 °C for 4 hours under a nitrogen atmosphere. The generated TiO₂ nanocrystals were homogenously distributed inside a porous carbon framework. With an extremely low Pt catalyst loading (0.04-0.1 wt%), the obtained porous catalyst could effectively oxidize formaldehyde to CO₂ and H₂O even under room temperature (conv. ∼100%). Wood acted as both a structural template and reduction agent for Pt catalyst generation in sintering. Therefore, no post H₂ reduction treatment for catalyst activation was required. The hierarchal channel structures, including 2-10 nm mesopores and 20 μm diameter channels, could be controlled by calcination temperature and atmosphere, which was confirmed by SEM and BET characterizations. Based on the abundant availability of wood templates and reduced cost for low Pt loading, this preparation method shows great potential for large-scale applications.

Fig. 1. Schematic illustration of wood templated biomimetic TiO₂/C hybrid material preparation.

Fig. 2. SEM images of TiO₂/C material containing biomimetic channels prepared by a wood template after sintering at 400 °C (A–D), 500 °C (E) and 600 °C (F).

Fig. 3. XRD patterns of the obtained TiO₂ material sintered at 400, 500 and 600 °C for 4 hours (o denotes rutile phase and * denotes anatase phase).

Fig. 4. Nitrogen adsorption/desorption isotherm curves (A) and corresponding pore-size distribution curves (B) of prepared TiO₂ materials under different sintering temperatures.

Fig. 5. XPS survey spectra (A) of the obtained catalysts and high resolution spectra of Pt 4f (B), Ti 2p (C) and O 1s (D) of prepared TiO₂ samples under different sintering temperatures.

Fig. 6. TGA curves of wood samples impregnated with TiO₂ and catalyst precursors. (A) Constant temperature at 400 °C for 1 hour under air atmosphere; (B) 500 °C; (C) 600 °C.

Fig. 7. Catalytic oxidation of formaldehyde over prepared porous TiO₂ catalyst material. (A) The HCOH concentration in upstream and downstream of reactor bed by using different prepared catalysts. (B) The CO₂ and CO measurements in the reaction of wood templated catalyst (0.092% Pt content, calcined at 400 °C). (C) Performances of catalysts with 400–600 °C calcination temperatures. (D) Performances of catalysts (0.092% Pt content, calcined at 400 °C) under different reaction temperatures and air humidities. (E) Conversions of catalysts with different Pt loading amounts. (F) Long time durability test.

Fig. 8. Schematic illustration of reactant and product diffusion in wood templated catalyst (A) and possible mechanism diagram for HCHO oxidation (B).