Can json_encode trigger a catch block?

No but you can check it's return value in a function and throw an exception when something goes wrong. You can also use json_last_error to get details on the error

Example:

function my_json_encode($data) {
    if( json_encode($data) === false ) {
        throw new Exception( json_last_error() );
    }
}

try {
    my_json_encode($data);
}
catch(Exception $e ) {
    // do something
}

I do find it highly annoying that to get the actual error message you have to check a list of constants that is returned from json_last_error(). In the past I've used a switch / case statement to make that happen but you could throw different exceptions depending on the error.