Process optimisation and structural insights on single-atom tungsten catalyst production under varied annealing with tungsten precursor

Abstract

The precise control of a single atomic site has been a significant concern in the field of single-atom catalysts. However, research on the effect parameters or factors that influence the matrix material is limited, yet it plays a crucial role in understanding how single-atom catalysts behave. In this study, one of the key parameters for synthesising a single-atom tungsten catalyst is discussed to optimise the yield of an active site. Variations in the involved parameters, such as the stoichiometry ratio, annealing temperature, annealing duration, tungsten complex ion formation, and rapid mixing of tungsten to produce the precursor, were examined. The stoichiometric ratio was set at Pt: W with a 17:1 ratio. Alkali treatment was applied after annealing to remove oxide by-products and to promote electronic delocalisation for single-atom formation. X-Ray diffraction (XRD) spectra showed that the structure of Pt displayed peaks at 39.7°, 67.5°, and 46.1°, while peaks for W₂C were observed at 40° and 46°, and WC spectra showed a peak at 84°. Variations in reaction time during tungsten complex ion formation led to changes in crystal phases caused by the formation of tungsten alkoxide, which affects the growth of crystallinity and the altered aggregation pattern. XRD results indicated that annealing at 650°C and 700°C for 2 hours likely facilitated the formation of a single-atom tungsten catalyst. The volume of methanol used during the reaction on tungsten complex ions showed that 10 mL provided better formation of tungsten alkoxide, especially with sonication mixing for 30 seconds. The durations of tungsten alkoxide formation revealed that 10 and 15 minutes yielded the best reaction times, characterised by low intensity and broader peaks. A template synthesis for the single-atom catalyst is reported to aid understanding.