Table 2. Box–Behnken Design Matrix with Three Independent Variables for the Experimental and Predicted Pd Selectivity Coefficient Values.

	independent variables						dependent variable
	coded values			real values			selectivity coefficient
run	X1	X2	X3	ECH (%)	pH	ECH (%)	βexp	βpred
1	–1	–1	0	0.10	1.0	0.55	100.98 ± 0.70	98.74
2	+1	–1	0	1.00	1.0	0.55	18.04 ± 1.21	18.97
3	–1	+1	0	0.10	2.4	0.55	67.71 ± 0.17	66.78
4	+1	+1	0	1.00	2.4	0.55	19.45 ± 0.94	21.69
5	–1	0	–1	0.10	1.7	0.10	62.42 ± 2.03	64.51
6	+1	0	–1	1.00	1.7	0.10	19.09 ± 0.06	18.00
7	–1	0	+1	0.10	1.7	1.00	90.12 ± 2.36	91.21
8	+1	0	+1	1.00	1.7	1.00	14.96 ± 1.83	12.87
9	0	–1	–1	0.55	1.0	0.10	31.63 ± 2.35	31.78
10	0	+1	–1	0.55	2.4	0.10	26.23 ± 0.15	25.07
11	0	–1	+1	0.55	1.0	1.00	49.32± 1.20	50.48
12	0	+1	+1	0.55	2.4	1.00	28.10 ± 0.71	27.95
13	0	0	0	0.55	1.7	0.55	28.12 ± 0.41	27.06
14	0	0	0	0.55	1.7	0.55	24.72 ± 1.85	27.06
15	0	0	0	0.55	1.7	0.55	27.23 ± 0.56	27.06
16	0	0	0	0.55	1.7	0.55	26.91 ± 0.42	27.06
17	0	0	0	0.55	1.7	0.55	28.31 ± 2.10	27.06