Natural Gas Steam Reforming over Rhodium/Alumina Catalysts: Experimental and Numerical Study of the Carbon Deposition from Ethylene and Carbon Monoxide

Abstract

Natural gas steam reforming (SR) over technically used rhodium/alumina (Rh/Al 2 O 3 ) honeycomb catalysts is studied experimentally at temperatures between 923 and 1073 K and steam-to-carbon ratios (S/C) of unity, with regard to coke deposition caused by the decomposition of the product species ethylene (C 2 H 4 ) and carbon monoxide (CO). Furthermore, the process is modeled using detailed reaction mechanisms, and numerical simulations are carried out to describe the coke formation on Rh/Al 2 O 3 catalysts quantitatively. The amount of deposited carbon was detected and analyzed for varying feed mixtures of the products CO and C 2 H 4 diluted in N 2 . During the decomposition of CO, the saturation of the amount of coke is monitored by feeding CO in high concentrations. No saturation occurs for the same amounts of coke resulting from the decomposition of C 2 H 4 . The coking rate caused by the decomposition of C 2 H 4 is found to be ∼25 times higher than the coking rate caused by the decomposition of CO. The differences in coking behavior caused by C 2 H 4 and CO, respectively, are described by coking models.

Microkinetic model validation for Fischer-Tropsch synthesis at methanation conditions based on steady state isotopic transient kinetic analysis

“…The surface species chemisorption enthalpies are calculated via the UBI-QEP method [93][94][95]. This methodology is extensively applied in fundamental microkinetic modeling studies [41,[96][97][98][99][100][101] to relate the surface species chemisorption enthalpies to atomic chemisorption enthalpies. In this work, the latter are the chemisorption enthalpies of H, C and O, which are considered as three additional adjustable model parameters.…”

On thermodynamic equilibrium of carbon deposition from gaseous C-H-O mixtures: updating for nanotubes

“…Several authors ( Rostrup-Nielsen 1972, 1984, Jankhah et al 2008, Cimenti and Hill 2009, Essmann et al 2014 highlighted that both the thermodynamic equilibrium conditions and the kinetic rate of all reactions and phase transitions should be considered in predictions of carbon deposits. However, Rostrup-Nielsen and Christiansen (2011) showed that the equilibrium constants for methane decomposition decisively depend on the metal catalyst type and stated that "[t]he important question is whether or not carbon is formed and not the rate at which it may be formed."…”

A Single-Event MicroKinetic model for the cobalt catalyzed Fischer-Tropsch Synthesis

“…Chemisorption enthalpies for the various surface species are calculated via the UBI-QEP method [27][28][29], which is widely used in fundamental microkinetic modeling studies [70][71][72][73][74][75][76][77]. This method relates the chemisorption enthalpy of a species to the atomic chemisorption enthalpies of H, C and O.…”