Applied Catalysis A: General 218 (2001) 181–188 Coke characterisation in aged residue hydrotreating catalysts by solid-state 13 C-NMR spectroscopy and temperature-programmed oxidation M.A. Callejas a , M.T. Mart´ ınez a,∗ , T. Blasco b , E. Sastre c a Instituto de Carboqu´ ımica CSIC, Apartado 589, 50080 Zaragoza, Spain b Instituto de Tecnolog´ ıa Qu´ ımica, UPV-CSIC, Avda. de los Naranjos s/n, 46022 Valencia, Spain c Instituto de Catálisis y Petróleoqu´ ımica CSIC, Campus UAM-Cantoblanco, 28049 Madrid, Spain Received 9 January 2001; received in revised form 23 April 2001; accepted 25 April 2001 Abstract A long term (7400 h) petroleum residue hydroprocessing study was conducted with a view to gain a clear understanding of the nature of the coke that deposits on the catalyst surface during the operation and to investigate the influence of processing time on coke build-up. Elemental analysis of the catalysts showed a rapid coke build-up on the catalyst surface during the early hours of the run, reaching as high as 12.4 wt.% within 100 h, and a maximum value between 1100 and 2100 h. From 2100 h, it was showed a significant decrease of the carbon content reaching a stable value from 3100 h. The enhanced nitrogen content of the coke deposits suggested that asphaltene fractions containing nitrogen were concentrated on the catalyst in the initial operation period. Additionally, the coke deposits on the spent catalysts were investigated using C-13 solid-state nuclear magnetic resonance techniques of cross-polarisation with magic-angle spinning (CP-MAS) for characterising the aromatic and aliphatic carbon types. Nuclear magnetic resonance (NMR) spectra revealed an increase of the aromaticity with a further increase of time on stream and the removal of aliphatic reversible carbon from the catalysts. Temperature-programmed oxidation (TPO) study showed the existence of different profiles, which characterised the reac- tivity of the deposits on the catalysts. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Petroleum fraction hydrotreating; Deactivation; Coke deposition; Temperature-programmed oxidation; NMR spectra 1. Introduction Catalyst deactivation is an important fact in petrochemical and petroleum industries, both from an economics and technological point of view. The loss of catalyst activity makes necessary either to stop the unit to regenerate the catalyst, or to adopt differ- ∗ Corresponding author. Fax: +34-976733318. E-mail address: mtmartinez@carbon.icb.csic.es (M.T. Mart´ ınez). ent technologies such as alternately swinging out a reactor from the reactor train for regeneration or with continuous regeneration of the catalyst moving from reaction to regeneration zones. In supported metal catalysts, metal sintering during coke oxidation com- plicates regeneration, and therefore a redispersion and reduction step must be carried out. Coke deposition on the catalyst is generally believed to be the primary cause of catalyst deactivation in hydrotreating petroleum distillates [1,2]. In order to 0926-860X/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0926-860X(01)00640-8