Abstract
The effect of heating method employed for drying and calcination during the synthesis of 1 wt% Pt/Al2O3 catalyst was investigated. Conventional heating (CH) in resistive oven and microwave heating (MW) in single mode were applied, and the Pt dispersion and Brunauer-Emmett-Teller (BET) surface area were measured to characterize the samples. It was evidenced that the fast and homogeneous heating offered by the microwave heating led to higher Pt dispersion. However, this benefit was only achieved when the subsequent calcination was performed in a conventional oven. The aging in microwave oven of conventionally prepared—as well as MW-prepared—catalysts demonstrated the great ability of microwave irradiation to accelerate platinum sintering. After 1 h at 800 °C under microwave, catalysts showed a dispersion of 5%. Therefore, microwave treatment should be considered for accelerated catalyst aging but should be avoided as a calcination technique for the synthesis of highly dispersed Pt/Al2O3.
Highlights
A common method to prepare supported noble metal catalyst is wet impregnation
The drying time was determined by microwave heating (MW) drying of wetted alumina. 15 min appeared sufficient to evaporate all water from the alumina pores, which was controlled by weighing the alumina after drying
To study the impact of microwave thermal treatment on Pt dispersion, a set of 1 wt% Pt/Al2 O3 samples was prepared with different combinations of drying and calcination methods
Summary
A common method to prepare supported noble metal catalyst is wet impregnation. It consists in impregnating a porous metal oxide, with a high surface area, with a solution of noble metal precursor. The solvent is evaporated by a slow drying step while the remaining compounds from the metal complex are decomposed by high temperature calcination These two steps are crucial for the resulting metal distribution and metal particle size. To control the metal deposition uniformity and the metal particle size it is necessary to limit the transport phenomena observed during drying in a conventional furnace based on resistive heating, called Joule heating With this aim, other ways of drying impregnated catalysts have been used such as spray drying [3] and freeze-drying [4,5], yielding high initial dispersion. It has been shown that microwave drying leads to a more uniform distribution of metal particles than regular oven drying in the case of Ni/Al2 O3 catalyst [2,6,7] These results were explained by the unique volumetric heating provided by microwaves. The impact of microwave drying and calcination on the resulting platinum dispersion was compared with conventional drying and calcination
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