I'm trying to create a cronjob on my synology system using the info provided in this error report

So, I run this cron job with user root:
php70 /volume1/web/freshrss/app/actualize_script.php > /volume1/web/freshrss/cron.txt 2>&1

And this is the outpot of the logfile:

Starting feed actualization at 2017-12-08T10:08:53+01:00
Actualize YannickV...
PHP Fatal error: Uncaught Error: Undefined class constant 'MYSQL_ATTR_INIT_COMMAND' in /volume1/web/freshrss/lib/Minz/ModelPdo.php:65
Stack trace:
#0 /volume1/web/freshrss/app/actualize_script.php(62): Minz_ModelPdo->__construct('YannickV')
#1 {main}
thrown in /volume1/web/freshrss/lib/Minz/ModelPdo.php on line 65
Results:
YannickV

The pdo_mysql extension is activated in the options. Anyone with idea's?

Thx!
Yannick