Believing is being convinced of something more than one doubts it, believing greater than 50%, and therefore believing it sufficiently to act commensurately with that conviction.
Knowing is being 100% certain of something, believing it without doubting, believing it 100%, and therefore acting commensurately with that conviction.
Lying is being unconvinced of something but claiming to believe it to be true.
The idea of knowingly choosing to believe a lie seems to me, therefore, to be a logically impossibility.
One could knowingly choose to profess to believe a lie.