Buying excessive concentrations of lively websites and sustaining their secure constructions at excessive temperatures have at all times been a major problem in catalyst design [1], [2], [3]. In supported nanocatalysts, the sintering of nanoparticles at excessive temperatures usually results in irreversible deactivation [4], [5], leading to a decline within the catalytic exercise. The migration and aggregation of cell species from small nanoparticles to massive nanoparticles, often known as Oswald ripening, is thermodynamically pushed by the variations in floor free power [2]. Theoretically, this sintering course of will be mitigated by regulating the free power of the nanoparticles or slicing off the migration pathway of the cell species [6]. Impressed by this, alloying [7], [8], spatial confinement [5], [9], geometric shielding [10], and metal-support interplay [11], [12], [13] have been developed to assemble sintering-resistant nanocatalysts. Lately, this concept has been additional developed right into a reverse ripening technique through which the trapping of cell metallic species utilizing acceptable substrates redisperse massive nanoparticles into small nanoparticles and even single atoms. For instance, Dayte and Wang et al. developed thermally secure single-atom platinum-on-ceria catalysts [14] and two-dimensional rafts of PdOx [15] through atom trapping. Xiao and coworkers noticed a discount within the dimension of copper nanoparticles (∼5.6 to ∼2.4 nm) in dealuminated beta zeolite after publicity to methanol vapor at 200 °C. This characteristic reversed the overall sintering channel, leading to strong catalysts for dimethyl oxalate hydrogenation to ethylene glycol at 400 °C with practically 100 % conversion and selectivity for 200 h [16].
Regardless of the appreciable progress within the design of extremely dispersed metallic or metallic oxide catalysts [17], as a result of deep understanding of metal- and oxide-substrate interplay, the interplay between metallic salts and oxide substrates was much less understood [18], [19]. Specifically, the metallic salts are extensively used because the lively element or the precursors of the metallic (oxide) catalysts in a wide range of catalysis processes similar to oxidative coupling of methane (OCM) [20]. Nevertheless, a number of essential points stay to be clarified on this necessary system as a result of lack of atomic-level structural evolution proof. As an example, the interplay mechanism between the metallic salts and totally different substrates below the elevated temperature was scarcely explored. Whether or not and the way the dispersion course of and stability of the supported metallic salts catalysts might be exactly manipulated continues to be an open query. Lately, in-situ transmission electron microscopy has been used and achieved many necessary progresses within the research of the catalyst structural evolution below varied exterior environments [21], [22], [23], [24], [25], [26], which offers an unprecedented alternative to disclose the underlying structural evolution mechanism of metallic salts catalysts on the nanoscale.
On this work, we report a direct visualization of a substrate-dependent clustering of Na2WO4 through in-situ transmission electron microscopy (TEM). Particularly, Na2WO4 evolves from massive bulk particles to evenly distributed high-concentration nanoclusters on the ZrO2 floor however maintains its bulk construction on the TiO2 floor at excessive temperatures. X-ray photoelectron spectroscopy (XPS) research and density practical concept (DFT) calculations recommend that this substrate-dependent structural evolution is pushed by the various interplay between Na2WO4 and the substrate. Utilizing methyl chloride-to-vinyl chloride (MCTV) as a probe response, we display the nice affect of the structural evolution of Na2WO4 in figuring out the catalytic efficiency.
