Should a student mention about contacting a faculty in a SOP even if the faculty has not replied yet?
I would recommend against mentioning e-mail contact with faculty unless you've had a substantive interaction, one that leads you to believe they would remember you and support your application.  In particular, you don't want someone on the admissions committee to mention to a colleague "So, I hear applicant X has been in touch with you; what was your impression?" and receive the reply "I have no idea who that is."

If there has been no reply to your e-mail, you could still indicate interest in your statement of purpose ("Based on my interests in X and Y, I envision Professors A and B as possible advisors.").  This would help classify the application and indicate who should look at it, without setting up the expectation that they will already know who you are.