try this:
<h2 class="featured-title"><a href="http://siteurl.com/category/<?php echo strtolower(str_replace(" ","",$arr[$i]["title"])); ?>"><?php echo esc_html($arr[$i]["title"]); ?></a></h2>
try this:
<h2 class="featured-title"><a href="http://siteurl.com/category/<?php echo strtolower(str_replace(" ","",$arr[$i]["title"])); ?>"><?php echo esc_html($arr[$i]["title"]); ?></a></h2>