Search

The integrated carbon capture and conversion (ICCC) is a promising catalytic process to produce syngas from CO2 and CH4 via a combined separation and reactor unit. Besides, its performance can fluctuate from the inconsistent feed ratio resulting from the flue gas unit. Herein, the Ratings concept based on density functional theory (DFT) is applied to overcome these problems in a two‐step protocol: (i) catalyst identification, which designates the catalyst characteristics and predicts performance based on reactivity (RT−R) and stability (RT−S) Ratings calculated based on activation energies obtained either from experiments or DFT, and (ii) catalyst optimization that optimized a catalyst's performance via the determination of new operating condition accounted for its deactivation over time. Moreover, temperature and feed ratio sensitivity were investigated, revealing that most catalysts are more sensitive to temperature change than the feed ratio. [ABSTRACT FROM AUTHOR]

Methane dehydroaromatization (MDA) over Mo/HZSM‐5 has been hypothesized in literature to proceed via a two‐step mechanism: methane is first converted to ethylene on the molybdenum (Mo) functionality and then ethylene is oligomerized, cyclized and dehydrogenated on the Brønsted acid sites (BAS) of the HZSM‐5 support. This hypothesis is tested by studying the conversion of ethylene at the same conditions as used for MDA, namely 700 °C, atmospheric pressure, and by co‐feeding experiments with H2 and CH4. Our results suggest that ethylene is not the main intermediate for MDA, because the aromatic selectivities obtained from methane conversion are higher than selectivities measured during ethylene conversion. Furthermore, carbonaceous deposits formed during MDA have a lower density, are more hydrogenated and more active than the ones formed during ethylene aromatization (EDA). Similarly as for MDA, an activation period in which Mo carburizes to its active phase and an induction period, in which aromatics formation rates increase to their maximum are observed for ethylene conversion. The induction period, which was explained by the buildup of a hydrocarbon pool (HCP) is much faster with methane than with ethylene. This period, is attributed to a slow buildup of hydrocarbons, strongly adsorbed on Mo sites, because it is only observed with catalysts containing Mo. Hydrogen co‐feeding with ethylene leads to the formation of more reactive coke species and a significantly prolonged lifetime of the catalyst, but not to a faster buildup of the HCP. [ABSTRACT FROM AUTHOR]

The deactivation of supported nickel catalysts by coking is an important technological subject for many chemical processes, especially when high concentrations of unsaturated hydrocarbons are present in the feed gas. Here, the reversible segregation of Ni from a LaFeO3±δ perovskite‐type host lattice was exploited to completely recover a LaFe0.8Ni0.2O3±δ catalyst after it had been deliberately subjected to severe carbon deposition during CO2 methanation in ethylene rich feed gas for several hours. Temperature programmed reduction, X‐ray diffraction, electron microscopy, X‐ray absorption spectroscopy and catalytic activity tests were used to follow the catalyst structure along the various steps of reduction, reaction, coking and subsequent regeneration, while Raman spectroscopy and electron microscopy were used to characterize the nature of the carbon deposits. It is shown that upon reduction Ni atoms segregate to the surface of the perovskite to form catalytic active Ni particles. Oxidation stimulates Ni atoms to readopt the coordination environment of Fe in the perovskite matrix. This property persisted after severe catalyst deactivation by filamentous, partially graphitic carbon. It is demonstrated that simple catalyst reoxidation can be applied to oxidize all carbon deposits while additionally reverting segregated Ni back into the host lattice, thus protecting Ni from particle growth and resultant long‐term loss of catalyst activity over multiple regeneration cycles. Recovery in the nick (el) of time! Complete recovery of a coked perovskite‐derived nickel methanation catalyst is demonstrated by exploiting the exceptional property of reversible segregation of nickel from the LaFeO3 host perovskite‐type oxide. The formation of active nickel particles under reducing conditions and moreover the reincorporation of the same by reoxidation results in highly redox stable nickel catalysts, which can be regenerated from coke deposition multiple times with no sign of long‐term degradation. [ABSTRACT FROM AUTHOR]

Abstract: Methane is converted over nickel on ceria zirconia (Ni/CZ) into ethane, aromatics, and hydrogen at steady state up to the thermodynamic limit at temperatures of 350 to 500 °C. At 450 and 500 °C, traces of ethylene are also produced. Ni/NiO particles activate methane and couple the resulting surface species to hydrocarbon products. Large Ni particles are responsible for the formation of carbonaceous deposits. Furthermore, aromatics are formed on these sites. Smaller Ni/NiO particles are responsible for the formation of ethane and ethylene and appear to provide sustained activity. It is suggested that these Ni sites are too small to assemble aromatic deposits, and hence they remain active throughout the reaction. [ABSTRACT FROM AUTHOR]

In their Research Article, S. Praserthdam and co-workers applied this concept for an on-line optimization of the Integrated Carbon Capture and Conversion (ICCC) process - a promising catalytic process that produces syngas from CO SB 2 sb and CH SB 4 sb via a combined separation and reactor unit in a two-step protocol: (i) catalyst identification that designates the catalyst characteristics and predicts performance based on reactivity (RT-R) and stability (RT-S) ratings and (ii) catalyst optimization that optimized a catalyst's performance via the determination of new operating condition accounted for its deactivation over time. Keywords: Catalyst Deactivation; Coking; Dry Reforming of Methane (DRM); First-principles; Syngas EN Catalyst Deactivation Coking Dry Reforming of Methane (DRM) First-principles Syngas 1 1 1 05/23/23 20230519 NES 230519 B The Front Cover b presented the Ratings concept as a tool for effective heterogeneous catalysts screening and optimization based on Density Functional Theory (DFT). Catalyst Deactivation, Coking, Dry Reforming of Methane (DRM), First-principles, Syngas. [Extracted from the article]

The catalytic performance of a Ni/MgAlOx catalyst was investigated in the high temperature CO2 reforming of CH4. The catalyst was developed using a Ni, Mg, Al hydrotalcite-like precursor obtained by co-precipitation. Despite the high Ni loading of 55 wt%, the synthesized Ni/MgAlOx catalyst possessed a thermally stable microstructure up to 900 °C with Ni nanoparticles of 9 nm. This stability is attributed to the embedding nature of the oxide matrix, and allows increasing the reaction temperature without losing active Ni surface area. To evaluate the effect of the reaction temperature on the reforming performance and the coking behavior, two different reaction temperatures (800 and 900 °C) were investigated. At both temperatures the prepared catalyst showed high rates of CH4 consumption. The higher temperature promotes the stability of the catalyst performance due to mitigation of the carbon formation. [ABSTRACT FROM AUTHOR]