Abstract
In this work, the activity of bimetallic Pd-Au doped hierarchically structured titania catalysts has been investigated in the total oxidation of toluene. In earlier works, doping titania with group Vb metal oxides ensured an increased catalytic performance in the elimination of VOC molecules. A synergy between gold and palladium loaded at the surface of titania supports provided better performances in VOC oxidation reactions. Therefore, the main focus in this work was to investigate the durability of the prepared catalysts under long time-on-stream periods. Vanadium-doped catalysts showed a stable activity throughout the whole 110 h test, whereas, surprisingly, niobium-doped catalysts presented a cycle-like activity while nevertheless maintaining a high performance in toluene elimination. Operando Diffuse Reflectance Infrared Fourrier Transform spectroscopy (DRIFT) experiments revealed that variations in the presence of OH radicals and the presence of carbonaceous compounds adsorbed at the surface of spent catalysts varies with the occurrence of oscillations. X-ray Photoelectron Spectroscopy (XPS) results show that interactions between the material and the active phase provided extra amounts of mobile oxygen species and participated in easing the reduction of palladium. An enhanced redox reaction scheme is thus obtained and allows the occurrence of the cyclic-like performance of the catalyst.
Highlights
The total oxidation of volatile organic compounds over noble metal-based catalysts has been widely studied in the past couple of decades to reduce atmospheric pollution produced by industrial emissions
PdAu5NbTi and PdAu5VTi catalysts previously tested in the total oxidation of toluene in increasing temperature were exposed to 110 h of a flowing toluene (1000 ppm) and air mixture at a low conversion rate (~15% conversion to CO2, T15(PdAu5NbTi) = 200 ◦ C and T15(PdAu5VTi) = 212 ◦ C)
Conversion rate, at which deactivation is more difficult to observe [13,24,25]. This deactivation can be caused by the formation and deposition of greater amounts of carbonaceous compounds induced by more incomplete combustion at this low conversion rate
Summary
The total oxidation of volatile organic compounds over noble metal-based catalysts has been widely studied in the past couple of decades to reduce atmospheric pollution produced by industrial emissions. Reviews discussing the use of palladium and gold-based mono or bimetallic catalytic systems for volatile organic compounds’ (VOC) removal or water-gas shit reactions can be found in the literature. Catalysts 2018, 8, 574 compared to that of monometallic catalysts. Enache et al [9,10] investigated gold and palladium catalysts supported on TiO2 in the oxidation of alcohols and aldehydes, and showed the effect of a synergy between both noble metals, leading to an increased activity and to a greater control of the selectivity in an oxidation reaction. They proved that a gold-rich core and shell-rich palladium morphology provides the best results in VOC elimination in terms of activity
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