In order to comprehensively investigate the effect of boron (B) and phosphorous (P) promoters on the catalytic performance of a hydrodesulfurization catalyst (NiMo/gamma-Al2O3, separate or simultaneous addition of the two promoters and the method of their addition to the catalyst solution or support have been studied by physical, chemical and reactor evaluation of nine synthetic catalysts using a diesel fuel feed containing 11,500 ppm of sulfur and 250 ppm of nitrogen. For better evaluation of the synthetic catalysts, their surface area, morphology, crystalline structure, regeneration temperature and acidity have been studied by ICP, XRD, Raman, FTIR, TPR, BET, FESEM and TPD analyses. Reactor evaluations have been performed at a temperature of 340 degrees C, pressure of 65 bar, LHSV of 0.8 h(-1) and hydrogen to hydrocarbon ratio of 250 and the amounts of sulfur and nitrogen resulting from each catalyst have been determined. The catalysts showed very different performances in the absence or presence of P and B promoters in the desulfurization and hydrodenitrogenation processes. The presence of P and B promoters seems to be necessary in the hydrodesulfurization process. However, the presence of P and B promoters in the HDN process depends on the type and method of the promoter addition. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.