It was narrated in some hadiths that the Sunnah prayer before Zuhr is two rak`ahs. In some other hadiths, it is narrated that Sunnah prayer before Zuhr is four rak`ahs (two-by-two).

A house will be built in paradise for every Muslim who offers twelve rak`ahs of optional prayer other than the obligatory prayer in a day and night, to seek the pleasure of Allah.

The correct opinion is that you can pray Tahiyyat al-Masjid at all times, even after Fajr and after ‘Asr because of the general applicability of the hadith “When any one of you enters the Mosque, he should not sit down until he has prayed two rak`ahs.”