Concentration-Dependent Evolution of the Belousov-Zhabotinsky Reaction as Determined by X-ray Absorption and UV-Vis Spectroscopies.

Although the Belousov-Zhabotinsky (BZ) chemical reaction has been the object of intense research efforts for almost a century, many aspects of the BZ complex oscillatory behavior still remain to be clarified, also due to difficulties in experimentally monitoring the speciation of the main brominated compounds during the reaction cycles. Herein, we describe an integrated approach based on Br K-edge X-ray absorption and ultraviolet-visible (UV-vis) spectroscopies to identify the onset and evolution of concentration-dependent collective bromine oscillations in the classical BZ reaction. Principal component analysis, multivariate curve resolution, and theoretical X-ray spectroscopy simulations were combined to identify the number, nature, and concentration time evolution of the key reaction brominated species during the chaotic and periodic BZ regimes. Our integrated approach enabled real-time monitoring of how variations in metal catalyst concentration influence both the metal center and key brominated BZ species throughout the different stages of the complex reaction pathway. The multidisciplinary experimental and theoretical approach, sensitive to both the brominated and metal portions of the BZ system, overcomes the challenges in detecting the spectroscopically silent BZ reaction species and may be applied to rationalize a wide range of BZ and non-BZ oscillatory reactions.