Coke Characterization on Pt/Al2O3−β-Zeolite Reforming Catalysts

Feasibility of bioleaching integrated with a chemical oxidation process for improved leaching of valuable metals from refinery spent hydroprocessing catalyst

Bioleaching is considered an eco-friendly technique for leaching metals from spent hydroprocessing catalysts; however, the low bioleaching yield of some valuable metals (Mo and V) is a severe bottleneck to its successful implementation. The present study reported the potential of an integrated bioleaching-chemical oxidation process in improved leaching of valuable metals (Mo and V) from refinery spent hydroprocessing catalysts. The first stage bioleaching of a spent catalyst (coked/decoked) was conducted using sulfur-oxidizing microbes. The results suggested that after 72 h of bioleaching, 85.7% Ni, 86.9% V, and 72.1% Mo were leached out from the coked spent catalyst. Bioleaching yield in decoked spent catalyst was relatively lower (86.8% Ni, 79.8% V, and 59.8% Mo). The low bioleaching yield in the decoked spent catalyst was attributed to metals' presence in stable fractions (residual + oxidizable). After first stage bioleaching, the integration of a second stage chemical oxidation process (1 M H₂O₂) drastically improved the leaching of Ni, Mo, and V (94.2-100%) from the coked spent catalyst. The improvement was attributed to the high redox potential (1.77 V) of the H₂O₂, which led to the transformation of low-valence metal sulfides into high-valence metallic ions more conducive to acidic bioleaching. In the decoked spent catalyst, the increment in the leaching yield after second stage chemical oxidation was marginal (<5%). The results suggested that the integrated bioleaching-chemical oxidation process is an effective method for the complete leaching of valuable metals from the coked spent catalyst.

Transition metal chalcogenide bifunctional catalysts for chemical recycling by plastic hydrocracking: a single-source precursor approach

Sulfided nickel, an established hydrocracking and hydrotreating catalyst for hydrocarbon refining, was synthesized on porous aluminosilicate supports for the hydrocracking of mixed polyolefin waste. Zeolite beta, zeolite 13X, MCM41 and an amorphous silica-alumina catalyst support were impregnated with the single-source precursor (SSP) nickel (II) ethylxanthate for catalyst support screening. Application of this synthesis method to beta-supported nickel (Ni@Beta), as an alternative to wet impregnation using aqueous nickel (II) nitrate, provided catalytic materials with higher conversion to fluid products at the same mild batch reaction conditions of 330°C with appropriate agitation and 20 bar H2 pressure. Mass balance quantification demonstrated that SSP-derived 5wt%Ni@Beta yielded a greater than 95 wt% conversion of a mixed polyolefin feed to fluid products, compared with 39.8 wt% conversion in the case of 5wt%Ni@Beta prepared by wet impregnation. Liquid and gas products were quantitatively analysed by gas chromatography-flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS), revealing a strong selectivity to saturated C4 (37.3 wt%), C5 (21.6 wt%) and C6 (12.8 wt%) hydrocarbons in the case of the SSP-derived catalyst.

Anti-coke behavior of an alumina nanosheet supported Pt–Sn catalyst for isobutane dehydrogenation

Alumina nanosheet supported platinum-based catalysts exhibited excellent catalytic reactivity and stability with an anti-coke capacity in the isobutane dehydrogenation process due to the abundant defect sites and decreased acidity.

Tuning partially charged Ptδ+ of atomically dispersed Pt catalysts toward superior propane dehydrogenation performance

An experimentally obtained volcano-type curve is observed for propane dehydrogenation over a group of atomically dispersed Pt catalysts on various supports. The oxidation state of Ptδ+ active sites plays a determining role in enhancing the activity.

Ring Enlargement of Methylcyclopentane over Pt/(HZSM-48+pseudoboehmite) Catalysts

Platinum catalysts loaded on a hybrid support, composed of HZSM-48 and pseudoboehmite, were applied to the synthesis of benzene through methylcyclopentane (MCP) reforming in order to investigate the effect of the addition of pseudoboehmite to Pt/HZSM-48 for ring-enlargement reaction. A total of 0.5 wt% of platinum was impregnated on the hybrid support by using the incipient wetness method. Catalyst characterization was performed with nitrogen sorption, X-ray diffraction, temperature-programmed desorption of NH3, and infrared spectroscopy of adsorbed pyridine. It was found that mesoporous structures were well-developed in Pt/(HZSM-48 + pseudoboehmite) catalyst as a result of the pseudoboehmite addition, of which the average pore size was in the range of 7–8 nm. The presence of pseudoboehmite in the catalyst increases the total amount of acid sites and weakens the acid strength, compared with those of the Pt/HZSM-48 catalyst. Lewis acid sites were more abundant than Brönsted acid sites over the Pt/(HZSM-48+pseudoboehmite) catalysts. It was found that selectivity to the ring-enlargement reaction is dominant over selectivity to the ring-opening reaction over the Pt/(HZSM-48 + pseudoboehmite) catalysts. The benzene yield over Pt/(HZSM-48 + pseudoboehmite, 1:1) catalyst reached 65.1% at 450 °C and 0.3 h−1. As well as being influenced by the mesoporous structure, the higher activity and selectivity in MCP reforming was also determined by appropriate acidity of the Pt/(HZSM-48 + pseudoboehmite) catalysts.

Propane dehydrogenation over Pt-Cu bimetallic catalysts: the nature of coke deposition and the role of copper

This paper describes an investigation of the promotional effect of Cu on the catalytic performance of Pt/Al2O3 catalysts for propane dehydrogenation. We have shown that Pt/Al2O3 catalysts possess higher propylene selectivity and lower deactivation rate as well as enhanced anti-coking ability upon Cu addition. The optimized loading content of Cu is 0.5 wt%, which increases the propylene selectivity to 90.8% with a propylene yield of 36.5%. The origin of the enhanced catalytic performance and anti-coking ability of the Pt-Cu/Al2O3 catalyst is ascribed to the intimate interaction between Pt and Cu, which is confirmed by the change of particle morphology and atomic electronic environment of the catalyst. The Pt-Cu interaction inhibits propylene adsorption and elevates the energy barrier of C-C bond rupture. The inhibited propylene adsorption diminishes the possibility of coke formation and suppresses the cracking reaction towards the formation of lighter hydrocarbons on Pt-Cu/Al2O3, while a higher energy barrier for C-C bond cleavage suppresses the methane formation.