Abstract Temperature-programmed oxidation (TPO), Raman spectrometry, and X-ray photoelectron spectroscopy (XPS) are used to characterize coke species deposited on a 0.61 wt% Pt/alumina catalyst for three reactions, carried out separately: partial oxidation (POX), steam reforming (SR), and autothermal reforming (ATR). Three individual compounds were used as simulants of liquid fuels in each of these three reactions: tetradecane, decalin, and 1-methylnaphthalene. The TPO profiles of the coke showed that partial oxidation and steam reforming resulted in generally greater coke deposition than autothermal reforming for each of the fuels. 1-Methylnaphthalene produces more coke than the other fuels in each of the reactions. Coke appears to be deposited both on the metal and the support, with the coke on the metal being more easily oxidized by TPO. Raman spectroscopy shows that there is no significant change in the carbon crystallite size on any of the catalysts; all are within the range of 1.45–1.83 nm. XPS analysis of carbon deposited during partial oxidation of tetradecane shows that small amounts of graphitic carbon (C/Al ratio

Characterization of carbon deposited on Pt/alumina catalyst during reforming of liquid hydrocarbons

Zeolites with ordered microporous systems, distinct framework topologies, good spatial nanoconfinement effects, and superior (hydro)thermal stability are an ideal scaffold for planting diverse active metal species, including single sites, clusters, and nanoparticles in the framework and framework-associated sites and extra-framework positions, thus affording the metal-in-zeolite catalysts outstanding activity, unique shape selectivity, and enhanced stability and recyclability in the processes of Brønsted acid-, Lewis acid-, and extra-framework metal-catalyzed reactions. Especially, thanks to the advances in zeolite synthesis and characterization techniques in recent years, zeolite-confined extra-framework metal catalysts (denoted as metal@zeolite composites) have experienced rapid development in heterogeneous catalysis, owing to the combination of the merits of both active metal sites and zeolite intrinsic properties. In this review, we will present the recent developments of synthesis strategies for incorporating and tailoring of active metal sites in zeolites and advanced characterization techniques for identification of the location, distribution, and coordination environment of metal species in zeolites. Furthermore, the catalytic applications of metal-in-zeolite catalysts are demonstrated, with an emphasis on the metal@zeolite composites in hydrogenation, dehydrogenation, and oxidation reactions. Finally, we point out the current challenges and future perspectives on precise synthesis, atomic level identification, and practical application of the metal-in-zeolite catalyst system.

Metal Sites in Zeolites: Synthesis, Characterization, and Catalysis.

HZSM-5, Co-incorporated HZSM-5 (3Co/Z5) and Co-incorporated hierarchical HZSM-5 (3Co/DZ5) were employed in catalytic reforming of volatiles from lignite pyrolysis in a drop bed reactor aiming at high yields of light aromatics. The co-effect of hierarchical pores and metallic sites on 3Co/DZ5 promoted the formation of benzene, toluene, xylene and naphthalene, and improved the service lifespan by decreasing coke formation. The influence of hierarchical pores and metallic sites on the deposition and nature of coke and on its location in the channels or/and the outer surface of zeolites was investigated. For 3Co/DZ5, the hierarchical pores retarded its deactivation by preventing internal coke formation while facilitating the external coke formation, owing to the reduced diffusion resistance of coke precursors (aromatic species) out of channels. The introduction of metallic sites brought the suppression of O-containing species depositing on zeolite. After continuous operation, the skeleton structures of both spent and regenerated catalysts were seriously damaged by coke deposition and sintering. The main causes of catalyst deactivation were assigned to two deactivating carbonaceous species with aromaticity and aliphaticity located on the inner pores and outer surface. The soluble long-chain aliphatics from coke extracts located on the outer surface were attributed to the decomposition of inherent aliphatic chain structure in lignite. The residual coke trended to graphite-like structure. The coking behavior was revealed by means of some technologies that the internal coke mainly had impact on the catalyst performance, especially for the insoluble aromatics with high polycondensation, whereas the external coke consumes the surface active sites, resulting in uninterrupted accumulation of coke precursors, eventually blocking the accessibility to channels.

Yang Li

Papers

Insights into coke location of catalyst deactivation during in-situ catalytic reforming of lignite pyrolysis volatiles over cobalt-modified zeolites

Encapsulation Ni in HZSM-5 for catalytic hydropyrolysis of biomass to light aromatics

Effect of coal ranks on light aromatics production during reforming of pyrolysis volatiles over HZSM-5 under Ar and H2-assisted atmospheres

Formation of Light Aromatics and Coke during Catalytic Reforming of Biopolymer-Derived Volatiles over HZSM-5