Bimetallic Co–Ni/Al 2O 3 catalyst for propane dry reforming: Estimation of reaction metrics from longevity runs

Abstract

Dry reforming of hydrocarbons is accompanied by carbon deposition making it difficult to unambiguously estimate the true reaction metrics (rate constant, yield and selectivity) without the masking effect of coke formation. This study employed a method originally proposed by Levenspiel [1999. Industrial & Engineering Chemistry Research 38, 4140–4143] to determine the intrinsic reaction rate simultaneously with the carbon-induced deactivation coefficient from transient rate data over an extended period of time (up to 72 h), for propane dry reforming over a Co–Ni catalyst at 823–973 K. The rate constant k ′ and deactivation coefficient, k d were determined from a fit of the concentration history data to the hyperbolic reaction–deactivation model for 1st-order kinetics in a plug flow reactor. However, the product H 2 : CO ratio was generally invariant with time over the 3-day period for different CO 2 : C 3 H 8 feed ratio values (4–7) but remained within a band of between 0.4 and 0.6. Both k ′ and k d exhibited a negative order dependency on the CO 2 : C 3 H 8 ratio at −0.575 and −2.39, respectively. Arrhenius treatment of these two reaction metrics also yielded activation energy estimates of 92.3 and 164.4 kJ mol −1 for the true reforming reaction and deactivation process, respectively. Catalyst characterization was carried out using XRF, liquid N 2 adsorption, XRD, H 2 chemisorption, temperature programmed desorption of NH 3 and CO 2 , temperature-programmed reduction (with H 2 ) and oxidation (with air) as well as solid TOC content analysis.