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A new sol-gel method that employs cation exchange from an aqueous metal ion solution with H+ ions of granulated alginic acid was developed for synthesizing high-purity Y2O3 nanoparticles. In this study, the cation exchange kinetics of H+~Y3+ in aqueous solution were analyzed using on-line pH technology and off-line inductively coupled plasma-atomic emission spectrometry (ICP-AES) analysis. Pseudo 2nd-order models were utilized to evaluate the parameters of the kinetics, suggesting that the concentration of H+~Y3+ involved in the cation exchange reaction was 1:1.733. Further, a comprehensive understanding of the Y-ALG calcination process was developed using thermo-gravimetric analysis, along with results obtained from differential scanning calorimetry (TGA/DSC). A detailed analysis of the XRD Rietveld refinement plots revealed that the crystallite sizes of Y2O3 nanoparticles were about 4 nm (500 °C) and 15 nm (800 °C), respectively. Differential pulse voltammetry (DPV) was employed to investigate the electrochemical oxidation of catechol. The oxidation peak currents of catechol at Y2O3 (500 °C)/GCE and Y2O3 (800 °C)/GCE showed two stages linear function of concentration (2.0~20.0 × 10−6 mol/L, 20.0~60.0 × 10−6 mol/L). The results indicated that the detection limits were equal to 2.4 × 10−7 mol/L (Y2O3 (500 °C)/GCE) and 7.8 × 10−7 mol/L (Y2O3 (800 °C)/GCE). The study not only provided a method to synthesize metal oxide, but also proposed a promising on-line pH model to study cation exchange kinetics. [ABSTRACT FROM AUTHOR]