The usual reason for doing this is to increase the reverse blocking voltage but it doubles the forward voltage and it can be problematic ensuring the reverse voltage is shared between each diode. In this case it's not a good idea and is completely unnecessary, as silicon and Schottky diodes with a higher reverse blocking voltage than 48V are widely available and aren't expensive.
If this is just a quick prototype and you're on a tight timescale. Order the correct components, then use two 40V diodes in series, just to get it working, whilst you're waiting for your order and replace them with the correct diodes, as soon as they arrive.