Cron restart apache2

As others pointed out, I would also suggest to find out the root cause.
However if you need to add a cronjob, use below

Code:

*/15 * * * * /root/restart_apache > /dev/null 2>&1

Add the entries below to the file /root/restart_apache and chmod it to 755

Code:

#!/bin/bash
/etc/init.d/httpd restart

Note: Use command 'crontab -e' to edit the crontab.