The temperature effect and basic structural features of a potassium catalyst supported on hydrothermal TiO2 were studied. The calcination of a 20% K/TiHT catalyst at temperatures higher than 600 degrees C, led to a change of the crystalline phase of potassium oxide into a potassium titanate. Despite the low surface area of the catalyst calcined at high temperature total conversion to methyl esters was achieved at 2 h of reaction. These results are explained by the presence of highly strong basic sites associated with the potassium titanate structure formed on these catalysts. (C) 2015 Elsevier Ltd. All rights reserved.