exclude by category?

I would like to display all posts other than the posts I have labelled featured. The following does not work:

<?php
$cat = get_categories( 'exclude' => 'featured');
$category = $cat->slug;
echo do_shortcode('[ajax_load_more post_type="post" scroll="false" category="'.$category.'"]');
?>

https://ww.wp.xz.cn/plugins/ajax-load-more/