Fatty nitriles have lately become of interest in the frame of biofuels or for the valorization of the oil part of biomass as fine chemicals such as polymers. The production of long-chain fatty nitriles by direct reaction of esters with ammonia has however not been academically extensively studied, although several catalysts were developed and published in patents. Acid-base features are implicitly considered as leading the catalysis of this reaction, but no direct correlation was investigated with any nature or number of acidic or basic sites. The present study aims at understanding which sites are responsible of this reaction and thus how to design better catalysts. Strong acidity correlates at 300 degrees C for ester conversion and nitrile yield, suggesting a common nature of the reaction among all kinds of catalysts. An upper strength limit, over which undesirable side-products appear, was evaluated, and the factors influencing the production of N-methyl amide were analyzed. (C) 2013 Elsevier Inc. All rights reserved.