Convergence problem with different mesh size

Dear Sir or Madam,

Sorry to disturb you. I was running a simple 1D transport model with surface complexation, but it never ends. However, I found it worked when I increased the mesh size from  ∆x =1.28E-4 m to ∆x =1.28E-2 m.

I attempted to revise my original refined model (since I need the refined mesh) by means of: 1) reducing the DELTEN and DELTMX; 2) changing the RCOUR; 3) changing the TOLTR and TOLCH. But all of them failed. Is there any other way I can try to revise it? Thank you!

Best regards,

Lang