Multisite wordpress help

Hi
I want to fetch posts from all the website on my multisite network only for few categories not all post. Here is my code which is working for fetching all the post but i don’t know to use loop in it.

$post_6 = get_blog_post(2, $i );
echo '<h2>'.$post_6->post_title.'</h2>';
echo '<p>'.$post_6->post_content .'</p>';
echo '<p>'.$post_6->post_excerpt.'</p>'

Problem in this code is that I can’t fetch post category by using $post_6->post_category it returns “Array”. any method so that i can get all the data from others website on network.