Featured Posts Slider Increase to 12

Hi I have transformed the grid in a slider through this code that works well:

function add_script_in_footer(){
?>
<script type="text/javascript" charset="utf-8">
    jQuery(document).ready(function(){
        var change_every = 7; // The number of seconds that the slider will auto-advance in
        var current = 1;
        function auto_advance(){
            if(current == -1) return false;
            jQuery('#featured-content .slider-next').eq(current % jQuery('#featured-content .slider-next').length).trigger('click', [true]);
            current++;
        };
        setInterval(function(){auto_advance()}, change_every * 1000);
    });
</script>
<?php
}
add_action('wp_footer', 'add_script_in_footer');

Now I would need to increase the number of featured posts to 12 or more. How do I remove this limit, this code does not work:

add_theme_support( 'featured-content', array(
		'featured_content_filter' => 'twentyfourteen_get_featured_posts',
		'max_posts' => 12,

	) );

Thanks