Two reactor designs with either passive or active thermal insulation were tested to produce synthesis gas from natural gas using catalytic partial oxidation on a system that exceeded laboratory scale. Preheating the working mixture significantly improves the conversion parameters. Preheating levels are limited by two factors: mixture ignition in the heater and overheating at the catalyst bed inlet area. The use of hot conversion products to provide active thermal insulation significantly improves the quality of the conversion. Because the same amount of identical catalyst was used in both reactors, the observed effect supports the hypothesis that the product composition depends primarily on the heat transfer process. (C) 2015 Elsevier B.V. All rights reserved.