robotframework open browser in remote server not work from web page

I've this use case: - robot and application server(apache+php) installed in a linux remote server - a web page that call robot file.

My robot file (demo.robot):

*** Settings ***
Library    Selenium2Library

*** Test Cases ***
Google search
        Set Environment Variable        webdriver.gecko.driver  /home/user/robot/geckodriver
         Set Environment Variable       webdriver.firefox.bin   /home/user/robot/firefox/firefox
        Open Browser    https://www.google.it   firefox

My php file:

<?php
$fff =shell_exec ('export DISPLAY=192.168.178.22:0.0 && export LD_LIBRARY_PATH=/usr/python-3.8.0/lib && export PATH=/usr/python-3.8.0/bin:/home/user/robot/geckodriver:/home/user/robot/firefox:/usr/bin/geckodriver:$PATH && cd /usr/www/httpd/htdocs/enm/ && robot ./demo/demoSuite.robot');
    $var =  "Esecuzione terminata";

?>

If I run robot file manually from shell it works fine:

robot -d demo/result demo/demo.robot

If I run the robot file from web page, it not works, the page is in a loop state without error. In The geckodriver-1.log there is no error:

1574886675597   mozrunner::runner       INFO    Running command: "/home/user/robot/firefox/firefox""-marionette""-foreground""-no-remote""-pro
file""/tmp/rust_mozprofileQAxKyX"

Where I wrong?

Thanks a lot