The initial value of k (log) was randomly selected from a range of 1 to 9, y1 was randomly selected from a range of 0 to 1, y2 was set equal to y1 plus a variable number between 0 and 1, y3 was set equal to y2 plus a variable number between 0 and 1, and values of y1, y2 and y3 were limited to the maximum in each normalized experimental data and 1. Different results were obtained by fitting different initial values, and the result with the smallest RMSE was selected as optimal parameters for each model. Finally, two sets of parameters were obtained for each reaction: k1, y1_k1, y2_k1, y3_k1 and k2, y1_k2, y2_k2, y3_k2.