The total acidity of reused CM-SO3H
decreased from 1.38 to 0.59 mmol/g after reuse for 3 cycles which
was resulted by the leaching of sulfonic acid and the coverage of
reaction compounds. The leaching of sulfonic acid was confirmed
by the decreasing of the NH3 desorption peak area of sulfonic at
250 C as shown in Fig. 4b.