Catalyst Deactivation by Carbon Deposition: The Remarkable Case of Nickel Confined by Atomic Layer Deposition

Abstract

In hydrocarbon reforming processes, coke formation on the catalyst usually reduces reaction rates. We show that when subjected to thermal treatment, a commercial nickel catalyst, overcoated with alumina, ALD exhibited both higher activity per g Ni and higher carbon formation rates than an uncoated catalyst. During the temperature-programmed reaction in a CH 4 + CO 2 atmosphere, the uncoated catalyst deactivated rapidly from carbon buildup, but the overcoated catalyst displayed an increase in catalytic activity per g Ni, despite generating two times the surface carbon. The unexpected phenomenon was investigated via TEM/EDS, TGA/DSC, SEM, XRD and Raman spectroscopy. We hypothesize that this may be due to (a) formation of a thicker than expected 'quasi-ALD' overcoat of amorphous alumina, (b) crystallization of ALD overcoat into nanofibers that act as secondary supports for migrating Ni, and (c) the ability of ALD overcoat to isolate carbon as carbon nanoonions (CNOs).

Atomic/molecular layer deposition strategies for enhanced CO2 capture, utilisation and storage materials

“…Applying metal oxide coatings via ALD onto existing catalysts represents another interesting approach to enhance catalytic performance in thermal reactions. It was proven that once metal oxides are 448,449,467,495 Through ALD, researchers applied various cycles of Al 2 O 3 onto Ni impregnated within different supports, subjecting these catalysts to elevated temperatures. Notably, the catalysts with a higher number of ALD cycles exhibited significantly elevated catalytic activity, achieving nearly complete conversion of both CO 2 and CH 4 , with a strong preference for producing CO and H 2 .…”

Methane-to-chemicals: a pathway to decarbonization

“…Several plants for CO 2 -rich steam reforming are currently in operation [ 53 ]. The catalysts are based on Ni and Ru on a basic support, often doped with Cu, while the engineering of the catalyst support also plays an important role [ 52 , 54 , 55 ]. However, in the absence of steam the catalysts described above suffer from deactivation.…”

Formation of a Porous Crystalline Mg1‐xAl2Oy Overlayer on Metal Catalysts via Controlled Solid‐State Reactions for High‐temperature Stable Catalysis

“…Dehydration, carbon species removal or combination of these two processes at high temperatures has been frequently applied to generate cracks/pores within oxide overlayers [2a,6b,h] . However, such thermal cracking often lacks control, leading to either poor stability or low activity due to the poor permeability of overlayers in a number of cases [6e–g] . Consequently, the development of a method for the tuning of porosities within overlayers is highly desirable to simultaneously achieve a sintering‐ and coking‐resistant catalyst with appreciable activity.…”