в urlrewrite.php

array(
        "CONDITION" => '#^/catalog/([/\-_.a-zA-Z0-9]+)/(.*?)\.html#',
        "RULE" => "SECTION_PATH=$1&ELEMENT_CODE=$2",
        "ID" => "bitrix:catalog.section",
        "PATH" => "/catalog/index.php",
    ),
    array(
        "CONDITION" => '#^/catalog/([/\-_.a-zA-Z0-9]+)/#',
        "RULE" => "SECTION_PATH=$1&$2",
        "ID" => "bitrix:catalog.section",
        "PATH" => "/catalog/index.php",
    ),
    array(
        "CONDITION" => "#^/catalog/#",
        "RULE" => "",
        "ID" => "bitrix:catalog.section",
        "PATH" => "/catalog/index.php",
    ),