wc-products-displayed-per-page.php

/**
 * Change number of products that are displayed per page (shop page).
 */
function wb_loop_shop_per_page( $cols ) {
	// $cols contains the current number of products per page based on the value stored on Options -> Reading.
	// Return the number of products you wanna show per page.
	$cols = 9;
	return $cols;
}
add_filter( 'loop_shop_per_page', 'wb_loop_shop_per_page', 20 );