Are there any Sahabas (RA) mentioned by name/title in Quran? Is there any thing in Quran regarding the greatness of Sahabas (RA)?

1. There are no Sahaaba (Radhiallaahu Anhum) mentioned specifically by name in the Qur'aan besides Hadhrat Zayd ibn Haarith (Radhiallaahu Anhu) pertaining to a lengthy incident. (Surah 33 Aayat 37).
There are many verses regarding the virtues of the Sahaaba (Radhiallaahu Anhum) in general. The meaning of one such comprehensive verse is, 'The first to lead the way from the Muhaajireen and the Ansaar and those who followed them in goodness. Allah is well pleased with them and they are well pleased with Him and Allah has made ready for them gardens underneath which rivers flow wherein they will abide forever. That is the supreme triumph.' (Surah9 verse 100)
In this verse, Allah Ta'ala announces that He is well pleased with the Sahaaba and that they too are well pleased with Him. Allah Ta'ala has guaranteed them all Jannat.
2. There are fifteen things which Allah Ta'ala made Shari'ah (law) in accordance to the opinion of Umar (Radhiallaahu Anhu). Thirteen of which are verses which Allah Ta'ala revealed in the Qur'aan and the remaining two in the Tawraat. The thirteen in the Qur'aan are:
a. To perform Salaat behind the Maqaam-e-Ibraahim (Surah 1 verse 125). b. The women should don the Hijaab (Surah 33 Aayat 67)
c. The prisoners of war in the battle of Badr should be killed (Surah 8 verse 67)
d. The incident in which Umar (Radhiallaahu Anhu) advised the wives of Nabi (Sallallaahu Alayhi Wasallam) not to cause him (Nabi) any inconvenience (Surah 66 Aayat 5)
e. In the same incident, when the prophet (Sallallaahu Alayhi Wasallam) went into seclusion, then Umar (Radhiallaahu Anhu) consoled the prophet (Sallallaahu Alayhi Wasallam) by saying, 'Allah is with you, Jibraaeel (Alayhis salaam), myself, Abu Bakr (Radhiallaahu Anhu) and the believers are all with you.' Allah Ta'ala revealed a verse accordingly. (Surah 66 verse4) f. Not to perform Janaaza Salaat for the hypocrites (Surah 9 Aayat 84) g. Not to seek forgiveness for the hypocrites (Surah 63 Aayat 6) h. The praises of Umar (Radhiallaahu Anhu) for Allah Ta'ala about how he created man through different stages (Surah 23 Aayat 14)
i. The incident of Ifk - Allah Ta'ala revealed a verse showing the freedom of Aaisha (Radhiallaahu Anha) in accordance to the statement of Umar (Radhiallaahu Anhu), i.e. 'Glory be to Allah, this is a great slander.' (Surah 24 Aayat 16)
j. The incident in which Umar (Radhiallaahu Anhu) tells a Jew that if the qualities of Nabi (Sallallaahu Alayhi Wasallam) are present in their book, why will they refuse to accept him. (Surah 2 Aayat 97-98)
k. Prohibition of liquor (Surah 2 Aayat 219)
l. Slaves should seek permission to the master's home (Surah 24 aayat 58) m. These verse, 'A large group of people will enter paradise' (Surah 56 Aayat 40) was revealed after Umar (Radhiallaahu Anhu) complained to Nabi (Sallallaahu Alayhi Wasallam) about why only a few people will gain salvation in the hereafter.

As for the two in the Tawraat, they are:
a) A Jew asked Umar (Radhiallaahu Anhu), Allah Ta'ala says in the Qur'aan that the width of Jannat is as large as the distance between the earth and the sky, so where is Jahannum? Umar (Radhiallaahu Anhu) asked the other Sahaaba to answer him, to which nobody did. Umar (Radhiallaahu Anhu) himself replied, 'When daylight comes, does it not cover the entire atmosphere between the earth and the sky?' the Jew said, 'Yes'. Umar (Radhiallaahu Anhu) said, 'Then where is night?' The Jew acknowledged this, took an oath and said that this is exactly what the Tawraat said.
b) Once a Jew recited a verse from the Tawraat in the presence of Umar (Radhiallaahu Anhu). Thereafter, Umar (Radhiallaahu Anhu) said to the Jew, 'Except he who takes stock of himself.' The Jew took an oath and said that, 'O Umar, this statement of yours is found in the same sequence in the Tawraat.' (Bukhaari pg.706 footnote No.7; Qadeemi)

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai