https://forum.opencartbrasil.com.br/viewtopic.php?f=50&t=14532

valdeir_categories.ocmod.xml

<?xml version="1.0" encoding="utf-8"?>
<modification>
  <name>Categories Page Product</name>
  <code>valdeir_categories</code>
  <version>1.0</version>
  <author>Valdeir Santana</author>
  <link>https://www.valdeirsantana.com.br</link>
  <file path="admin/controller/catalog/product.php">
	<operation>
      <search>
        <![CDATA[$data['products'][] = array(]]>
      </search>
      <add position="before">
        <![CDATA[$category_name = $this->db->query("SELECT cd.name FROM `" . DB_PREFIX . "category_description` cd LEFT JOIN `" . DB_PREFIX . "product_to_category` pc ON (pc.category_id = cd.category_id) WHERE cd.language_id = ".(int)$this->config->get('config_language_id')." AND pc.product_id = ".(int)$result['product_id']." ORDER BY cd.category_id DESC LIMIT 1");]]>
      </add>
    </operation>
	
	<operation>
      <search>
        <![CDATA['quantity'   => $result['quantity'],]]>
      </search>
      <add position="after">
        <![CDATA['category_name' => isset($category_name->row['name']) ? $category_name->row['name'] : "Sem Categoria",]]>
      </add>
    </operation>
  </file>
  
  <file path="admin/view/template/catalog/product_list.tpl">
	<operation>
		<search><![CDATA[<td class="text-right"><?php if ($sort == 'p.price') { ?>]]></search>
		<add position="before"><![CDATA[<td class="text-right">Categorias</td>]]></add>
	</operation>
	
	<operation>
		<search><![CDATA[<td class="text-right"><?php if ($product['special']) { ?>]]></search>
		<add position="before"><![CDATA[<td class="text-right"><?php echo $product['category_name'] ?></td>]]></add>
	</operation>
  </file>
</modification>