Abstract
The application of ceramic foams as structured catalyst supports is clearly expanding due to faster mass/heat transfer and higher contact efficiency than honeycomb monoliths and, mainly, packed beds. In this paper, alumina open-cell foams (OCFs) with different pore density (20, 30 and 40 ppi) were coated with Rh/CeO2 catalyst via a two steps synthesis method involving: (i) the solution combustion synthesis (SCS) to in-situ deposit the CeO2 carrier and (ii) the wet impregnation (WI) of the Rh active phase. The catalytic coatings were characterized in terms of morphology and adhesion properties by SEM/EDX analysis and ultrasounds test. Permeability and form coefficient were derived from pressure drop data. Catalytic performance was evaluated towards biogas Steam Reforming (SR) and Oxy-Steam Reforming (OSR) processes at atmospheric pressure by varying temperature (800–900 °C) and space velocity (35,000–140,000 NmL·g−1·h−1). Characteristics time analysis and dimensionless numbers were calculated to identify the controlling regime. Stability tests were performed for both SR and OSR over 200 h of time-on-stream (TOS) through consecutive start-up and shut-down cycles. As a result, homogenous, thin and high-resistance catalytic layers were in situ deposited on foam struts. All structured catalysts showed high activity, following the order 20 ppi < 30 ppi ≈ 40 ppi. External interphase (gas-solid) and external diffusion can be improved by reducing the pore diameter of the OCF structures. Anderson criterion revealed the absence of internal heat transfer resistances, as well as Damköhler and Weisz-Prater numbers excluded any internal mass transfer controlling regime, mainly due to thin coating thickness provided by the SCS method. Good stability was observed over 200 h of TOS for both SR and OSR processes.
Highlights
Bio-economy is a sustainable solution to meet the challenges of food security, resource scarcity, energy demand and climate change by efficient production of bio-resources and their conversion into food, bio-energy and biomaterials [1]
open-cell foams (OCFs) are composed of cell units which are repeated in all space dimensions; cells are the void part enclosed by struts and interconnected pores (Figure 1a)
OCFs showed a variation in pore size with increasing pore density which further influenced the other geometric and catalytic characteristics
Summary
Bio-economy is a sustainable solution to meet the challenges of food security, resource scarcity, energy demand and climate change by efficient production of bio-resources and their conversion into food, bio-energy and biomaterials [1]. Process intensification (PI) is a promising strategy to develop more competitive and sustainable processes in a transition towards a bio-based economy. The most interesting technological approach in heterogeneous catalysis is the application of structured catalysts (e.g., monoliths and foams) which paves a way for more energy and resources through efficient chemical transformations [4,5]. Monolith- and foam-structured catalysts are widely used in environmental applications for controlling both automotive and stationary emissions [6]. They are increasingly under development for many reaction applications, such as highly endothermic and exothermic reactions (hydrogenation, combustion or reforming processes) especially at low contact time [7,8]
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