With the aim to reduce greenhouse emissions, the recent perspectives of research are now focused not only on the development and optimization of technologies for carbon dioxide sequestration (CCS), but mainly on the conception and demonstration of new strategies for carbon dioxide utilisation (CCU) for the production of bulk chemicals or fuels [1]. In this context, particular attention has been paid on the direct catalytic hydrogenation of CO2 into dimethyl ether (DME), an environmentally friendly fuel compatible with use in conventional diesel engines [2-4]. From a catalytic point of view, the direct DME synthesis is boosting an intense research effort in the development and application of novel multi-functional hybrid systems, wherein a mix of different active sites are in close interaction among them to facilitate the rate of mass transfer of a reaction intermediate towards the final product. In this work, monolithic catalysts prepared by 3D printing are proposed as novel systems characterized by controllable and precise architectures that are unable to be made through conventional processes [1,5]. In particular, a series of CuZnZr-zeolite hybrid monoliths was prepared by a highly adaptable inhouse 3D printing system that allows uniform and sufficient distribution of the active catalytic material [6]. This involves the direct (co)extrusion of a catalyst-containing paste and a co-catalyst through a syringe mounted on a x,y,z stage. Fine tuning of the preparation conditions also includes the selection of printing variables such as the nozzle opening (fibre thickness), the type of nozzle (fibre shape), the inter-fibre distance (pore size) and the stacking of the layers (architecture) followed by sintering. The 3D printed monoliths were tested in the one-pot CO2-to-DME hydrogenation process (30 bar, 200- 260°C), in a tubular fixed catalyst bed reactor (i.d., 14 mm; l., 250 mm), with cylinder of various compositions, diameter 9 mm, length 50 mm and porosity (voidage) 30%. Figure 1 shows how the 3D-printed systems achieve an interesting catalytic performance, in terms of CO2 conversion and DME yield, with values at 260 °C comparable to those reached on conventionally prepared systems (22% and 9% respectively).Evidently, the operative conditions play a fundamental role in shifting the equilibrium towards the formation of MeOH/DME at expense of CO, due to a proper extent of metal-oxide interface for CO2 activation induced by the preparation procedure, easy accessibility of acidic sites to drive MeOH dehydration and controlled Cu° particle size to depress the formation of side products. These preliminary findings suggest the effectiveness of 3D-printing in the design of hybrid multi-site systems, owing to the capability of a full control of texture, structure, morphology and surface properties of the catalytic system necessary for scale-up and possible industrial exploitation.
Effectiveness of 3D-printed hybrid metal-zeolite monoliths for the direct CO2-to-DME hydrogenation
S Todaro;C Cannilla;A Mezzapica;F Frusteri;G Bonura
2021
Abstract
With the aim to reduce greenhouse emissions, the recent perspectives of research are now focused not only on the development and optimization of technologies for carbon dioxide sequestration (CCS), but mainly on the conception and demonstration of new strategies for carbon dioxide utilisation (CCU) for the production of bulk chemicals or fuels [1]. In this context, particular attention has been paid on the direct catalytic hydrogenation of CO2 into dimethyl ether (DME), an environmentally friendly fuel compatible with use in conventional diesel engines [2-4]. From a catalytic point of view, the direct DME synthesis is boosting an intense research effort in the development and application of novel multi-functional hybrid systems, wherein a mix of different active sites are in close interaction among them to facilitate the rate of mass transfer of a reaction intermediate towards the final product. In this work, monolithic catalysts prepared by 3D printing are proposed as novel systems characterized by controllable and precise architectures that are unable to be made through conventional processes [1,5]. In particular, a series of CuZnZr-zeolite hybrid monoliths was prepared by a highly adaptable inhouse 3D printing system that allows uniform and sufficient distribution of the active catalytic material [6]. This involves the direct (co)extrusion of a catalyst-containing paste and a co-catalyst through a syringe mounted on a x,y,z stage. Fine tuning of the preparation conditions also includes the selection of printing variables such as the nozzle opening (fibre thickness), the type of nozzle (fibre shape), the inter-fibre distance (pore size) and the stacking of the layers (architecture) followed by sintering. The 3D printed monoliths were tested in the one-pot CO2-to-DME hydrogenation process (30 bar, 200- 260°C), in a tubular fixed catalyst bed reactor (i.d., 14 mm; l., 250 mm), with cylinder of various compositions, diameter 9 mm, length 50 mm and porosity (voidage) 30%. Figure 1 shows how the 3D-printed systems achieve an interesting catalytic performance, in terms of CO2 conversion and DME yield, with values at 260 °C comparable to those reached on conventionally prepared systems (22% and 9% respectively).Evidently, the operative conditions play a fundamental role in shifting the equilibrium towards the formation of MeOH/DME at expense of CO, due to a proper extent of metal-oxide interface for CO2 activation induced by the preparation procedure, easy accessibility of acidic sites to drive MeOH dehydration and controlled Cu° particle size to depress the formation of side products. These preliminary findings suggest the effectiveness of 3D-printing in the design of hybrid multi-site systems, owing to the capability of a full control of texture, structure, morphology and surface properties of the catalytic system necessary for scale-up and possible industrial exploitation.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
