Thermal Deactivation of Rh/α-Al2O3 in the Catalytic Partial Oxidation of Iso-Octane: Effect of Flow Rate

Abstract

Catalytic partial oxidation (CPO) of logistic fuels is a promising technology for the small-scale and on-board production of syngas (H2 and CO). Rh coated monoliths can be used as catalysts that, due to Rh high activity, allow the use of reduced reactor volumes (with contact time in the order of milliseconds) and the achievement of high syngas yield. As the CPO process is globally exothermic, it can be operated in adiabatic reactors. The reaction mechanism of the CPO process involves the superposition of exothermic and endothermic reactions at the catalyst inlet. Thus, a hot spot temperature is formed, which may lead to catalyst deactivation via sintering. In this work, the effect of the flow rate on the overall performance of a CPO-reformer has been studied, using iso-octane as model fuel. The focus has been on thermal behavior. The experimental investigation consisted of iC8-CPO tests at varying total flow rates from 5 to 15 NL/min, wherein axially resolved temperature and composition measurements were performed. The increase of flow rate resulted in a progressive increase of the hot spot temperature, with partial loss of activity in the entry zone of the monolith (as evidenced by repeated reference tests of CH4-CPO); conversely, the adiabatic character of the reformer improved. A detailed modelling analysis provided the means for the interpretation of the observed results. The temperature hot spot can be limited by acting on the operating conditions of the process. However, a tradeoff is required between the stability of the catalyst and the achievement of high performances (syngas yield, reactants conversion, and reactor adiabaticity).

Environmental catalysts advance focused on lattice oxygen for the decomposition of harmful organic compounds

“…When exhaust gas contains high concentrations and high amounts of organic compounds (e.g., toluene), catalysts are often exposed to unpredictably high-temperature conditions (>1000 °C) by isolated combustion heat. 64) As conventional Pt based catalysts are generally deactivated at such temperatures due to aggregation and particle growth of Pt, it is desirable to develop catalysts with high thermal durability. Although the Pt/CeO 2 -ZrO 2 -Bi 2 O 3 /.-Al 2 O 3 catalyst is effective in oxidizing toluene, 57) .-Al 2 O 3 has low thermal durability (transition temperature: 9800 °C) 65) and is thus unsuitable for the support of the refractory catalyst.…”

Catalyst Deactivation, Poisoning and Regeneration

“…Some regeneration strategies [11,16], together with solutions to prevent or limit deactivation phenomena [7,9,11,16], are also discussed. Eventually, one review paper [20] analyzes the rich chemistry of rhodium/phosphine complexes, which are applied as homogeneous catalysts to promote a wide range of chemical transformations, showing how the in situ generation of the active species, as well as the reaction of the catalyst itself with other components in the reaction medium, can lead to a number of deactivation phenomena.More in detail, the effect of the gas flow rate on the formation of hotspots during the Catalytic Partial Oxidation of logistic fuels on Rh-based monoliths for the on-board production of syngas is investigated in [6]. Solutions to prevent the irreversible thermal deactivation of Ni/ZrO 2 catalysts during the Dry Reforming of Methane are proposed in [7] by inhibiting the transition of ZrO 2 into its monoclinic phase via modification with La.…”

“…More in detail, the effect of the gas flow rate on the formation of hotspots during the Catalytic Partial Oxidation of logistic fuels on Rh-based monoliths for the on-board production of syngas is investigated in [6]. Solutions to prevent the irreversible thermal deactivation of Ni/ZrO 2 catalysts during the Dry Reforming of Methane are proposed in [7] by inhibiting the transition of ZrO 2 into its monoclinic phase via modification with La.…”