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in catalog.xml, directly under:

Catalog Category (Non-Anchor) AND <label>Catalog Category (Anchor)</label>

<reference name="root">
            <action method="setTemplate"><template>page/1column.phtml</template></action>
        </reference>
        <!-- <reference name="left">
            <block type="catalog/layer_view" name="catalog.leftnav" before="-" template="catalog/layer/view.phtml"/>
        </reference> -->

http://woshka.com/blog/cms/shop-e-commerce/magento/how-to-change-category-layout-from-3-columns-to-2-columns-left-or-right-in-magento.html