Effect of mass transfer limitations on catalyst performance during reduction and carburization of iron based Fischer-Tropsch synthesis catalysts

Existence of intraparticle mass transfer limitations under typical Fischer-Tropsch synthesis has been reported previously,but there is no suitable study on the existence of intraparticle diffusion limitations under pretreatment steps (reduction and activation) and their effect on catalytic performance for iron based catalysts.In this study,Fe-Cu-La-SiO2 catalysts were prepared by co-precipitation method.To investigate the intraparticle mass transfer limitation under reduction,activation and reaction steps,and its effect on catalytic performance,catalyst pellets with different sizes of 6,3,1 and 0.5 mm have been prepared.All catalysts were calcined,pretreated and tested under similar conditions.The catalysts were activated in hydrogen (5%H2in N2) at 450℃ for 3 h and exposed to syngas (H2/CO=1) at 270℃ and atmospheric pressure for 40 h.Afterwards,FTS reaction tests were performed for approximately 120 h to reach steady state conditions at 290℃,17 bar and a feed flow (syngas H2/CO=1) rate of 3 L/h (STP).Using small pellets resulted in higher CO conversion,FT reaction rate and C5+ productivity as compared with larger pellets.The small pellets reached steady state conditions just 20 h after starting the reaction.Whereas for larger pellets,CO conversion,FT reaction rate and C5+ productivity increased gradually,and reached steady state and maximum values after 120 h of operation.The results illustrate that mass transfer limitations exist not only for FTS reaction but also for the reduction and carburization steps which lead to various phase formation through catalyst activation.Also the results indicate that some effects of mass transfer limitations in activation step,can be compensated in the reaction step.The results can be used for better design of iron based catalyst to improve the process economy.

Cathodic activated stainless steel mesh as a highly active electrocatalyst for the oxygen evolution reaction with self-healing possibility

The oxygen evolution reaction(OER)represents one of the major bottlenecks for broad-based applications of many clean energy storage/conversion technologies.The key to solving this problem lies in developing high-performing,cost effective and stable catalysts for the OER.Herein,we demonstrate that ubiquitous stainless steel mesh(SSM)materials activated by a facile cathodization treatment can be employed as a high performing OER catalyst,as showcased by the impressively low overpotentials of 275 and 319 mV to reach the benchmark current densities of 10 and 100 mA cm^−2(1.0 M KOH),respectively.Cathodized SSM also exhibits excellent performance in a two-electrode water electrolyzer,which requires a low cell voltage of 1.58 at 10 mA cm^−2 and outperforms many of water electrolyzers using earth-abundant OER catalysts.Moreover,cathodized SSM with minor performance degradation after the stability test can also be readily healed by subjecting it to an additional cathodization treatment.It is disclosed that the superior performance of cathodized SSMs stems from the surface enrichment of OER active Ni(oxy)hydroxide,facile gas-bubble removal and transportation over the unique mesh-structured surfaces,while the abundant reservoir of nickel in the bulk allows healing of the catalyst by a facile cathodization.

Kinetic study of propane dehydrogenation and catalyst deactivation over Pt-Sn/Al_2O_3catalyst

The kinetics of propane dehydrogenation and catalyst deactivation over Pt-Sn/Al2O3 catalyst were studied.Performance test runs were carried out in a fixed-bed integral reactor.Using a power-law rate expression for the surface reaction kinetics and independent law for deactivation kinetics,the experimental data were analyzed both by integral and a novel differential method of analysis and the results were compared.To avoid fluctuation of time-derivatives of conversion required for differential analysis,the conversion-time data were first fitted with appropriate functions.While the time-zero and rate constant of reaction were largely insensitive to the function employed,the rate constant of deactivation was much more sensitive to the function form.The advantage of the proposed differential method,however,is that the integration of the rate expression is not necessary which otherwise could be complicated or impossible.It was also found that the reaction is not limited by external and internal mass transfer limitations,implying that the employed kinetics could be considered as intrinsic ones.

Pulsed electrochemistry:A pathway to enhanced electrocatalysis and sustainable electrosynthesis

This review delves into pulsed electrochemistry,a new technique that is becoming an essential tool in the field of electrocatalysis and electrosynthesis.Unlike traditional potentiostatic methods,pulsed electrochemical approaches provide dynamic control over catalytic reactions,leading to better selectivity,efficiency,and stability across a range of applications.We examine the underlying theory of pulsed electrocatalysis and explore how waveform characteristics,potential,and pulse time affect catalytic processes.The review pays special attention to its application in key areas such as organic electrosynthesis,CO_(2) reduction reactions,and water splitting,explaining how pulsed techniques improve reaction conditions to boost yields and selectivity.Meanwhile,we focus on the technique’s impact on catalyst surface modulation,managing local interface environments,and addressing issues like catalyst deactivation and mass transfer limitations.Ultimately,this review highlights the transformative potential of pulsed electrochemistry in driving various electrocatalysis and electrosynthesis applications and sets the stage for future exploration and optimization of these electrochemistry systems.