Answered by Sayyidi al-Ḥabīb `Umar bin Hafīẓ (may Allāh preserve him and benefit us by him).

What can a student recite in order to keep his intentions pure and to banish laziness and procrastination at the time of study?

You should read the merits of seeking knowledge. There is a very useful section on this in the introduction to Imam al-Nawawi’s al-Majmu’. You should also study the biographies of those who exerted great efforts in seeking knowledge.

Read 100 times a day:

هُوَ اللهُ الَّذي لا إِلهَ إِلا هو عَالِمُ الغَيْبِ والشَّهادَةِ هُوَ الرَّحْمَنُ الرَّحِيم

Huwa Allāhu’lladhī la ilāha illā hu, ‘Ālimu’l ghaybi w’al-shahādah, Hu al-raḥmānu’ raḥīm

He is Allah, there is no god other than Him, knower of the unseen and the seen, He is the All-Compassionate, the All-Merciful. (Al- Ḥashr, 59:22)