Regeneration of single-atom catalysts deactivated under acid oxygen reduction reaction conditions

Single-atom catalysts serve as a promising candidate to realize noble-metal-free electrocatalytic oxygen reduction in acid media.However,their poor stability under working conditions strictly restrains their practical applications.Therefore,regeneration of their electrocatalytic activity is of great significance.Herein,the regeneration of a Fe-N-C single-atom catalyst is demonstrated to be feasible by a facile annealing regeneration strategy.The activity after regeneration recovers to that of the pristine electrocatalyst and surpasses the deactivated electrocatalyst.The regeneration mechanism is identified to be selfetching of the surface carbon layer and consequent exposure of the previously buried single-atom sites.Furthermore,the regeneration strategy is applicable to other single-atom catalysts.This work demonstrates the feasibility of regenerating oxygen reduction electrocatalysts and affords a pioneering approach to deal with rapid deactivation under working conditions.

Regeneration of Spent Catalyst and Impregnation of Catalyst by Supercritical Fluid

The possibility and feasibility of using supercritical fluid СО2 extraction process have been investigated and described in the book as part of the task of spent catalysts regeneration. The analysis of deactivating compounds has been carried out for industrial catalysts such as: 1) palladium catalyst G-58E of ethane-ethylene fraction hydrogenation;2) nickel/kieselguhr catalyst of process of separating acetylenic compounds from isoprene;3) active aluminum oxide catalyst of methyl phenyl carbinol dehydration process;4) palladium catalyst LD-265 of hydrocarbons hydrogenation process;5) nickel-molybdenum catalysts DN-3531 and Criterion 514 of kerosene hydrotreating process. The results of the study of catalyst deactivating compounds solubility in pure supercritical carbon dioxide and supercritical carbon dioxide are modified with polar additive. The results of the solubility study are described using the Peng-Robinson equation of state. The results of the implementation of the supercritical fluid СО2 extraction process with respect to deactivated industrial catalyst samples have been provided. A comparison of the characteristics of samples of catalysts regenerated using the traditional approach and the SC-CO2 extraction process has been conducted. The possibility of using supercritical fluid CO2 impregnation process in the synthesis of a palladium catalyst has been investigated. The synthesis of palladium chloride-based organometallic complexes has been carried out. The results of the study of solubility thereof in supercritical carbon dioxide have been provided. A dynamic supercritical fluid CO2 impregnation process condition has been implemented. A comparison of the characteristics of palladium catalyst samples synthesized using the conventional approach and SC-CO2 impregnation process has been conducted and presented in the book.

Plasma-chemical Synthesis and Regeneration of Catalysts for CH_4 Steam Conversion

We carried out experimental studies concerning the plasma-chemicalsynthesis(PCS) of a catalyst for CH_4 steam conversion and designed and built the equipment for PCSand/ or regeneration of spent catalyst for CH_4 steam conversion. Under the conditions of anelectric-arc low-temperature plasma (LTP), we studied the Ni-O-Al system and performed acomprehensive physicochemical analysis of the ultradispersed product obtained. It's the first timeworldwide when the conditions of plasma-chemical synthesis and/ or regeneration of CH_4 steamconversion catalysts under the conditions of electric-arc LTP are investigated depending on theplasma-chemical process (PCP) parameters and the plasma-chemical reactor (PCP) type (with CW-'coldwalls' T_W = 500 K or WW-'warm walls' T_W = 1500 K), samples with a specific surface of 120 m^2/gare obtained. Plasma-chemically synthesized and/ or regenerated samples have a homogenous chemicalcomposition similar to that the Girdller (USA) conventional industrial catalyst. It is empiricallyestablished that the optimal temperature range in PCR for synthesis of samples with maximumdispersity is (2000～3000) K. Results from investigation on dynamics and kinetics ofplasma-chemically synthesized and / or regenerated catalysts for CH4 steam conversion show thatunder LTP conditions premises for the formation of catalyst compositions are established. They arereduced 3 to 4 times faster than their industrial analogues. High specific surface of the samples,homogenous composition, high rate of active chemical surface formed by reduction, faulty crystallattice of catalytically active phases and mostly high catalytic activity make them a potentialcompetitor with their industrial analogues for their probable production in catalyst shops.

Coking and decoking chemistry for resource utilization of polycyclic aromatic hydrocarbons(PAHs)and low-carbon process

Low-carbon process for resource utilization of polycyclic aromatic hydrocarbons(PAHs)in zeolitecatalyzed processes,geared to carbon neutrality-a prominent trend throughout human activities,has been bottlenecked by the lack of a complete mechanistic understanding of coking and decoking chemistry,involving the speciation and molecular evolution of PAHs,the plethora of which causes catalyst deactivation and forces regeneration,rendering significant CO_(2) emission.Herein,by exploiting the high-resolution matrix-assisted laser desorption/ionization Fourier-transform ion cyclotron resonance mass spectrometry(MALDI FT-ICR MS),we unveil the missing fingerprints of the mechanistic pathways for both formation and decomposition of cross-linked cage-passing PAHs for SAPO-34-catalyzed,industrially relevant methanol-to-olefins(MTO)as a model reaction.Notable is the molecule-resolved symmetrical signature:their speciation originates exclusively from the direct coupling of in-cage hydrocarbon pool(HCP)species,whereas water-promoted decomposition of cage-passing PAHs initiates with selective cracking of inter-cage local structures at 8-rings followed by deep aromatic steam reforming.Molecular deciphering the reversibly dynamic evolution trajectory(fate)of full-spectrum aromatic hydrocarbons and fulfilling the real-time quantitative carbon resource footprints advance the fundamental knowledge of deactivation and regeneration phenomena(decay and recovery motifs of autocatalysis)and disclose the underlying mechanisms of especially the chemistry of coking and decoking in zeolite catalysis.The positive yet divergent roles of water in these two processes are disentangled.These unprecedented insights ultimately lead us to a steam regeneration strategy with valuable CO and H_(2) as main products,negligible CO_(2) emission in steam reforming and full catalyst activity recovery,which further proves feasible in other important chemical processes,promising to be a sustainable and potent approach that contributes to carbon-neutral chemical industry.

Regeneration of deactivated CeCoxO2 catalyst by simple thermal treatment

Active species loss owing to reactant stream washing is a general problem which industrial catalysts suffer from.In case of catalysts synthesized by co-precipitation method,which have active species unused in bulk phase,can be regenerated by a simple thermal treatment that leads to active species in bulk phase migration to surface of the deactivated catalysts.In this work,the influence of regeneration temperature was investigated by employing ammonium hydroxide washing to simulate reactant stream washing of CeCoxO2 catalysts for NO+CO reaction.It is found that the deactivated catalyst can be regenerated by simple thermal treatment and increasing calcination temperature could accelerate the Co species migration from the bulk phase to surface of catalysts.

Promoting effect of Zr on the catalytic combustion of methane over Pd/γ-Al2O3 catalyst

The effect of Zr on the catalytic performance of Pd/y-A1203 for the methane combustion was investigated. The results show that the addition of Zr can improve the activity and stability of Pd/γ-Al2O3 catalyst, which, based on the catalyst characterization （N2 adsorption, XRD, CO- Chemisorption, XPS, CHa-TPR and O2-TPO）, is ascribed to the interaction between Pd and Zr. The active phase of methane combustion over supported palladium catalyst is the Pd^0/Pd^2＋ mixture. Zr addition inhibits Pd aggregation and enhances the redox properties of active phase Pd^0/ Pd^2＋. H2 reduction could effectively reduce the oxidation degree of Pd species and regenerate the active sites （Pd^0/ pd^2＋）.