Mashreq bank (www.mashreqbank.com) has a interest free saving scheme called Mashreq Millionaire. Under this scheme one does not get interest but is eligible for a prize. You can get details from their web site. Should one hold these certificates and if yes are any winnings from this Halal?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

It is completely Haram to deposit your money in a usury-taking-bank, even if you do not receive interest, since this action constitutes a form of co-operation in sin and transgression. Allah, The Great and Almighty, forbids such an action saying: {…but do not help one another in sin and transgression. …} [5:2].
Furthermore, in case of necessity such as fearing to lose money and so on, one is allowed to deposit his/her money in such a bank.
But, if depositing money in such banks makes a depositor get benefit, then the transaction will be Haram due to (1) interest that one will get, and (2) its being a form of co-operation in sin and transgression.
In fact, depositing money in such banks is a form of lending money (to the bank) even if they call it "Deposit", because the bank will guarantee the money and this is the nature of "Loan", whereas there is no guarantee for "deposit" except in case of transgression or negligence since the bank here is a trustee.
Thus, depositing money in usury-taking-banks (such as al-Mashreeq, …) to receive a reward, is Haram since it is a form of loan than brings benefit.
Allah knows best.