Catalyst Synthesis Conditions Research Articles

Optimization of aluminum hydroxide catalyst for efficient hydrogen generation from aluminum-water reaction

Optimization of aluminum hydroxide catalyst for efficient hydrogen generation from aluminum-water reaction

Adaptive learning-driven high-throughput synthesis of oxygen reduction reaction Fe–N–C electrocatalysts

Adaptive learning-driven high-throughput synthesis of oxygen reduction reaction Fe–N–C electrocatalysts

A methodology for structure dependent global kinetic models: Application to the selective catalytic reduction of NO by hydrocarbons

• Structure sensitive catalytic reactions model. • SCR on Ag and Co catalysts, for NOx reduction. • Kinetic model with a single adsorbed species. Global kinetic models capable of capturing experimentally observed features of catalytic reactions are vital in design and optimization studies. In this work, a detailed analysis of the selective catalytic reduction of NO and NO 2 , particularly in automotive exhaust control is undertaken. The prominent metal based catalysts for this reaction range from Pt, Au & Rh to cheaper options including Cu, Ag & Co supported on Al 2 O 3 , SiO 2 , and occasionally, zeolites. Here, we focus on Ag & Co supported on Al 2 O 3 catalysts, and propose a computationally tractable kinetic model capable of capturing the observed SCR features across a range of catalyst synthesis and reactor operating conditions. In particular, the effects of metal loading on catalyst performance are closely examined. In SCR, an important aspect is the catalytic activity at higher inlet O 2 concentrations. The global kinetic model proposed here is shown to predict the trends with respect to reactor temperature and inlet feed compositions (including O 2 ), well, for both catalysts.

Low-Medium Temperature-Selective Catalytic Reduction of NO with NH3 over a Mn/Co-MOF-74 Catalyst.

To realize the selective catalytic reduction of NO at low–medium temperatures and avoid secondary pollution, a highly active catalyst Mn/Co-MOF-74 was synthesized. X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis, Brunauer–Emmett–Teller method, and scanning electron microscopy were employed to analyze the physicochemical properties of catalysts with different Mn/Co molar ratios and conjecture about the difference in the catalytic activity. Meanwhile, the effects of the molar ratio of Mn/Co, catalyst dosage, catalyst synthesis conditions, GHSV, and temperature on the NO conversion efficiencies were investigated and found that an optimal NO conversion efficiency of 93.5% was obtained at 200–225 °C. In the end, the stability of Mn/Co-MOF-74 was investigated and found that the catalyst has better sulfur and water resistance, and the NO conversion mechanism was speculated on the basis of characterizations and literature data.

Optimizing High-Throughput Synthesis of PGM-Free ORR Electrocatalyst Using Machine Learning Approach

Over the past decades, significant improvement has been achieved in the performance of platinum group metal-free (PGM-free) materials as an alternative to Pt-based electrocatalysts for oxygen reduction reaction (ORR). However, further progress in ORR activity requires new precursors and synthesis approaches. In response to this challenge, we generated a first of its kind experimental dataset of 36 samples using high-throughput synthesis and activity measurements. Numerous control parameters (e.g., Fe precursor identity, the precursor content, and pyrolysis temperature) were varied. We then developed several state-of-the-art machine learning (ML)-based regression models to predict ORR activity, dependent on selected synthesis variables. Through a novel iterative algorithm, higher prediction accuracy (smaller root-mean square error) was achieved. We identified that gradient boosting regression (GBR) and support vector regression (SVR), among several methods, work best for this dataset. Aided by our ML-based surrogate models, we decided to alter catalyst synthesis conditions, which resulted in a 36% increase in measured ORR activity in comparison to the maximum ORR mass activity value of 22 A/g catalyst in the original dataset. This combined experiment and machine learning approach represents a novel and promising path towards developing highly efficient next generation ORR electrocatalysts and, more generally, functional materials.

(Invited) In Situ Electron Microscopy Methods for Understanding Activity and Degradation in Fuel Cell Electrocatalysts

The scanning transmission electron microscope (STEM) is a powerful tool for imaging materials at the atomic scale. While imaging and spectroscopic analysis is typically performed at room temperature within the vacuum of the microscope, the last decade has seen a rapid development of micro-electromechanical system (MEMS)-based holders enabling a wide variety of in situ experiments, including heating in the presence of a gas and potential cycling within a liquid.[1,2] This talk will briefly review the pioneering efforts aimed at in situ observations of electrochemical materials along with the most recent evolutions in experimental, software and holder design for electrochemical materials.The talk will then focus on the application of in situ methods to fuel cell materials. We will first address atomically-dispersed platinum group metal-free (PGM-free) electrocatalysts derived from metal organic frameworks (MOFs). A critical step in the synthesis of these ORR catalysts is the high temperature heat treatment (up to 1100oC) required to convert the Fe, Ni, or Co-doped MOFs into graphitic carbons containing the proposed individual metal-nitrogen active sites.[3,4] In situ pyrolysis of the catalyst precursors was performed in a low-voltage, aberration-corrected STEM coupled with electron energy loss spectroscopy (EELS) to provide additional insight into the interaction between the metal-nitrogen sites and the graphitic carbon support. These experiments were correlated with in situ X-ray absorption spectroscopy (XAS) to demonstrate that active sites form in a lower temperature regime (600-800oC), but higher annealing temperatures are required to enhance graphitization of the carbon support, leading to increased performance in fuel cell tests.Enclosed environmental cells allow for heating in the presence of a gas at pressures up to 1 atmosphere and can be used to closely replicate catalyst synthesis conditions, as will be demonstrated on Pt-based catalyst in which annealing was performed under 100% hydrogen. A few studies to date have also explored fuel cell electrocatalyst degradation in liquid cells.[5-7] Such studies demonstrate the exciting potential for in situ electrochemistry, but are hindered by limited spatial resolution due to imaging through thick liquid layers and the long cycling times required to observe meaningful degradation. We take a step back from the challenging in situ experiments and use identical location (IL)-STEM to compare catalyst degradation mechanisms observed in the aqueous three electrode cell relative to tests performed on membrane electrode assemblies (MEAs). Like previous in situ and IL-STEM studies, coalescence mechanisms dominate in an aqueous environment, while Ostwald ripening is dominant in MEA tests.[8-10] We will discuss how sample preparation and cycling parameters can be adjusted to more closely replicate losses observed in fuel cell tests.[11]

Valorization of de-oiled microalgal biomass as a carbon-based heterogeneous catalyst for a sustainable biodiesel production

In this study, a novel carbon-based solid acid catalyst was synthesized by carbonization of de-oiled microalgal biomass followed by sulfonation. The effect of catalyst synthesis conditions such as carbonization temperature, sulfonation time, and H2SO4 concentration on the surface acidity of the catalyst and free fatty acid conversion was determined. The de-oiled microalgal biomass-based solid acid (DMB) catalyst was predominantly composed of carboxylic, phenolic, and sulfonic groups as indicated by the FTIR analysis and supported by the XPS analysis. The catalyst was further characterized by various methods to determine its physiochemical properties. A maximum fatty acid methyl ester (FAME) yield of 94.23% for microalgal oil (AO) and 96.25% for waste cooking oil (WCO) was obtained under optimized transesterification conditions. The catalyst exhibited high catalytic activity (FAME yield>90%) until the fourth cycle. Most of the biodiesel properties were within the permissible limit of EN 14,212 and ASTM D6751 standards.

Acai seed ash as a novel basic heterogeneous catalyst for biodiesel synthesis: Optimization of the biodiesel production process

In the present study, the catalytic activity of acai seed ash (ASA) was investigated for the synthesis of biodiesel from the methyl transesterification of soybean oil. Acai seeds were calcined at different temperatures (500–900 °C) and times (2–5 h) to determine the best catalyst synthesis conditions. The catalyst obtained by calcination at 800 °C for 4 h was characterized by thermogravimetric analysis (TG-DTG), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersion X-ray spectroscopy (EDS), and alkalinity. Subsequently, response surface methodology based on a face-centered composite design (FCCD 24) was applied to examine the best conditions to conduct the transesterification reaction. The optimal conditions were: temperature of 100 °C, molar ratio alcohol:oil of 18:1, catalyst concentration of 12.0% (w/w), and reaction time of 1 h, yielding biodiesel with an ester content of 98.5 ± 0.21%. The catalyst characterization showed that its catalytic activity is due to the high metal oxide content and carbonates with basic surface sites, making them highly efficient towards biodiesel production. The reuse of the catalyst showed that its catalytic activity resulted in an ester content above 92.5% in the first two reaction cycles. After the regeneration process, the catalyst yielded biodiesel with an ester content above 80.0% during four more reaction cycles. The production of a catalyst from acai seeds has several advantages, namely being obtained from widely available biomass waste, being low cost, and being easily synthesized, making it a sustainable and efficient catalyst for biodiesel production.

Effects of mordenite zeolite catalyst synthesis conditions on dimethyl ether carbonylation

Effects of different mordenite (MOR) zeolite synthesis conditions, such as salt additive, hydrothermal time, hydrothermal temperature, and ultrasonic assistance, on dimethyl ether (DME) carbonylation were studied systematically in this work. Salt as additives being introduced into hydrothermal system obviously promoted the crystallinity and morphology of MOR. With the increase of hydrothermal time and temperature, a better crystallinity was obtained on the sample. However, a higher hydrothermal temperature of 180 °C led to a slightly decreased crystallinity. The MOR catalyst with NaCl as the additive and hydrothermal treatment at 130 °C for 48 h realized a better DME carbonylation activity with 50% DME conversion and almost 100% methyl acetate (MA) selectivity. In addition, H-MOR-UT, a MOR zeolite prepared with the assistance of ultrasonic treatment, showed a special morphology consisting of lots of MOR nanosheets with a width of around 70 nm. Here, this H-MOR-UT realized an enhanced catalytic stability and the highest DME conversion of 70%, about 5 times higher than the reference MOR zeolite prepared by traditional method. The strikingly excellent catalytic performance was attributed to its more acid content, stronger acid strength and smaller grain size.

Utilisation of biomass wastes based activated carbon supported heterogeneous acid catalyst for biodiesel production

Abstract This study evaluated the utilisation of biomass wastes as catalyst supports by comparing the catalytic performance of papaya seed, empty fruit bunch (EFB) and corncob biomass waste derived carbon based acid catalysts applied for biodiesel production through esterification reaction of palm fatty acid distillate (PFAD) and methanol. Arylation of 4-benzenediazonium sulfonate synthesis method was able to sulfonate the catalyst support efficiently. The activated carbon (AC) synthesised possessed high porosity with surface area ranged between 639.68 and 972.66 m2/g. The effect of catalyst synthesising condition including carbonisation temperature (600–1000 °C), sulfonation time (0.5–2.5 h) and sulfanilic acid to AC weight ratio (3:1–13:1) towards the FAME yield and free fatty acid (FFA) conversion were evaluated. At the optimum catalyst synthesis conditions, corncob waste derived sulfonated AC catalyst exhibited the highest FAME yield and FFA conversion of 72.09% and 93.49%, respectively. Reusability study showed that corncob waste derived sulfonated AC catalyst was able to achieve relatively high FAME yield at the first two reaction cycles. The esterification reaction followed the irreversible pseudo-homogeneous reaction model. The high catalytic efficiency of the catalyst had shown its high potential to fit into the cost-effective and sustainable framework for biodiesel production.

Oxygen evolution activity limits the nucleation and catalytic growth of carbon nanotubes from carbon dioxide electrolysis via molten carbonates

Abstract Controlled catalytic synthesis of technologically valuable carbon nanomaterials by the electrochemical capture and conversion of CO2 is bottlenecked by limited understanding of combined electrochemical and catalytic mechanisms at play during conversion. Here, our findings provide new insight that a key factor for the electrochemical two-electrode catalytic growth of carbon nanotubes (CNTs) on the cathode surface is the oxygen evolution activity (OEA) occurring at the anode. Poor OEA can inhibit catalytic CNT formation altogether, while increased anode OEA is correlated to changes in diameter and crystallinity of CNTs with otherwise identical cathode catalyst layers and synthesis conditions. Specifically, comparing Cu, Ni/Al2O3, and Pt anodes with Fe/stainless steel cathodes we observe over 6x smaller CNT diameter distribution and over 2x lower D/G ratio when using Pt anodes with the highest OEA. This is attributed to the role of transport between the cathode and anode during synthesis; in the case of poor anode OEA, a build-up of oxide species near the cathode surface influences the surface tension at the catalyst-carbonate interface to modify CNT diameter and properties. This mechanistic insight opens the door to routes to controllably produce high quality carbon nanomaterials from the electrochemical capture and conversion of carbon dioxide.

Synthesis and Application of Heterogeneous Catalysts Based on Heteropolyacids for 5-Hydroxymethylfurfural Production from Glucose

This study aimed to evaluate the synthesis and application of heterogeneous catalysts based on heteropolyacids for 5-hydroxymethylfurfural (HMF) production from glucose. Initially, assays were carried out in order to establish the most favorable catalyst synthesis conditions. For such purpose, calcination temperature (300 or 500 °C), type of support (Nb2O5 or Al2O3), and active phase (H3PW12O40—HPW or H3PMo12O40—HPMo) were tested and combined based on Taguchi’s L8 orthogonal array. As a result, HPW-Nb2O5 calcined at 300 °C was selected as it presented optimal HMF production performance (9.5% yield). Subsequently, the reaction conditions capable of maximizing HMF production from glucose using the selected catalyst were established. In these experiments, different temperatures (160 or 200 °C), acetone-to-water ratios (1:1 or 3:1 v/v), glucose concentrations (50 or 100 g/L), and catalyst concentrations (1 or 5% w/v) were evaluated according to a Taguchi’s L16 experimental design. The conditions that resulted in the highest HMF yield (40.8%) consisted of using 50 g/L of glucose at 160 °C, 1:1 (v/v) acetone-to-water ratio, and catalyst concentration of 5% (w/v). Recycling tests revealed that the catalyst can be used in four runs, which results in the same HMF yield (approx. 40%).

Active learning-driven quantitative synthesis–structure–property relations for improving performance and revealing active sites of nitrogen-doped carbon for the hydrogen evolution reaction

A data-driven quantitative synthesis–structure–property relation methodology to elucidate correlations between catalyst synthesis conditions, structural properties and observed performance, providing a systematic way to optimize practical catalysts.

Hydrodechlorination and complete degradation of chlorinated compounds with the coupled action of Pd/SiO2 and Fe/SiO2 catalysts: Towards industrial catalyst synthesis conditions

Abstract In this study, Pd/SiO2 and Fe/SiO2 catalysts have been synthesized by the cogelation process for hydrodechlorination applications. Different synthesis conditions were tested to approach the industrial conditions using industrial grade reactants and ambient air drying. The influence of these changes has been studied on the texture and the catalytic activity of the catalysts. The resulting materials are composed of metallic (Pd catalysts) or metallic oxide (Fe catalysts) nanoparticles highly dispersed in porous silica. The catalysts present a high specific surface area (between 250 and 500 m2/g) with a large pore size range between micro-, meso- and macropores. The modifications of the synthesis conditions give catalysts with similar textural properties compared to lab-scale catalysts. The catalytic activity of the binary catalysts have been evaluated on the hydrodechlorination of the 2,4,6-trichlorophenol (TCP) in water. Results show that Pd/SiO2 catalysts are able to dechlorinate the TCP and that Fe/SiO2 materials are able to degrade the resulting phenol. So this process allows a complete degradation of TCP. Industrial conditions catalysts show also similar catalytic results compared to lab-scale catalysts for the hydrodechlorination of the 2,4,6-trichlorophenol (TCP) in water.

Application of Uniform Design Method in the Optimization of Hydrothermal Synthesis for Nano MoS2 Catalyst with High HDS Activity

The optimization of catalyst synthesis conditions using traditional single factor method involves extensive experimental time and costs. To overcome the drawbacks, a uniform design method was applied in the hydrothermal synthesis of nano MoS2 catalyst. An optimal synthesis condition is reached with only a few trials. Catalyst synthesis temperature is reduced to 200 °C. The catalyst synthesized at the screened condition shows high hydrotreating activities. The results conclude that the catalyst has thread-like slabs with a lattice structure that is less mature than fully developed MoS2. The characterization results indicate that the appearance of such structure may be due to the weak links of successive MoS2 nuclei. The high catalytic activity is a result of the layered structure and a significantly large number of defects on the slabs.

Effect of the Ni/Al2O3 Catalyst Synthesis Conditions at Application of the Solution Combustion Preparation Method on the Catalyst’s Properties and Efficiency in the Process of Nanofibrous Carbons Synthesis from Methane

Effect of the Ni/Al₂O₃ Catalyst Synthesis Conditions at Application of the Solution Combustion Preparation Method on the Catalyst’s Properties and Efficiency in the Process of Nanofibrous Carbons Synthesis from Methane

Power-to-Gas: Storing surplus electrical energy. Study of catalyst synthesis and operating conditions

Abstract Energy storage is needed in order to sustain the energy system on renewable energies like wind and solar power. Power-to-Gas (PtG) is a technology that enables the storage of the renewable electricity in a chemical carrier such as hydrogen, via water electrolysis, or methane, via carbon dioxide methanation. In this work a series of catalysts based on nickel and alumina, the catalyst commonly employed for carbon dioxide methanation, have been synthesised employing different calcination temperatures to study the influence of this parameter in the activity of the catalysts. As a result of this study 673 K was determined as the most suitable Moreover, the catalysts have also been tested at different pressures to determine the most suitable operating pressure. Although due to Le Chatelier's Principle a higher pressure results in an increasing yield, the study carried out proved that 10 bar is the most suitable pressure as the difference in the yield when increasing the pressure it is not high enough taking into account the costs and risks associated with higher pressures.

Synthesis-Structure-Activity Relationships in Co3O4 Catalyzed CO Oxidation.

In this work, a statistical design and analysis platform was used to develop cobalt oxide based oxidation catalysts prepared via one pot metal salt reduction. An emphasis was placed upon understanding the effects of synthesis conditions, such as heating regimen and Co2+ concentration on the metal salt reduction mechanism, the resultant nanomaterial properties (i.e., size, crystal structure, and crystal faceting), and the catalytic activity in CO oxidation. This was accomplished by carrying out XRD, TEM, and FTIR studies on synthesis intermediates and products. Additionally, high-throughput experimentation was employed to study the performance of Co3O4 oxidation catalysts over a wide range of reaction conditions using a 16-channel fixed bed reactor equipped with a parallel infrared imaging system. Specifically, Co3O4 nanomaterials of varying properties were evaluated for their performance as CO oxidation catalysts. Figure-of-merits including light-off temperatures and activation energies were measured and mapped back to the catalyst properties and synthesis conditions. Statistical analysis methods were used to elucidate significant property-activity relationships as well as the design rules relevant in the synthesis of active catalysts. It was found that the degree of grain boundary consolidation and anisotropic growth in fcc and hcp CoO intermediates significantly influenced the catalytic activity. By utilizing the discovered synthesis-structure-activity relationships, CO oxidation light off temperatures were decreased to <90°C.

Zeolite structure effects on Cu active center, SCR performance and stability of Cu-zeolite catalysts

Abstract In this study, comparative studies over nine NH3-SCR Cu-zeolites with different topologies were conducted. A clear trend was observed that the NH3-SCR performance was gradually improved with the zeolite-framework structures changing from straight-channel (ZSM-5, Beta, Y) to cage-type (SSZ-13, SSZ-16, SSZ-17), bridged by hybrid-structures (OFF-ERI series: Offretite, ZSM-34, UZM-12). Characterizations of the catalysts with XRD, XRF, XPS, UV–vis, NH3-TPD, and H2-TPR confirmed, under identical catalyst synthesis conditions, that the cage-type samples (Cu-SSZ-13, Cu-SSZ-16, and Cu-SSZ-17) possessed higher concentrations of strong acid sites and isolated Cu cations with respect to the straight-channel samples (Cu-ZSM-5, Cu-Beta, and Cu-Y). The cage-type catalysts showed superior SCR performance as compared to the straight-channel and hybrid types. This study corroborated the consensus from recent literature that a small cage aperture (∼3.8 A) is critical to prevent zeolite dealumination. Moreover, a clear correlation was found between zeolite acid strength and the nature of exchanged Cu species. Cage type zeolites with stronger acidity led to stabilization of isolated Cu ion monomers while dimeric Cu ions form in straight-channel zeolites with lower acidity. Catalysts with dominant monomeric active sites display more desirable SCR activity and selectivity to N2.

Highly Active and Durable Ir Catalyst for Oxygen Evolution Reaction for Proton Exchange Membrane Electrolysis

In the proton exchange membrane (PEM) water electrolysis, iridium (Ir) or iridium oxide (IrOx) black is the primary catalyst for the oxygen reduction reaction (OER) at the anode. Changing Ir black to Ir nanoparticles (3-4 nm) could significantly increase the catalyst activity of the OER and thus lowering the Ir loading. Under harsh PEM water electrolysis operating conditions, it is challenging to find electrically conductive and electrochemically stable supports to deposit Ir or IrOx nanoparticles The high operating potential, oxidation atmosphere and strong acid conditions has limited the application of carbon black, a most common support used in PEM fuel cells. In this work, iridium nanoparticles with a conductive chain was formed and deposited on high surface area tungsten doped TiO2 support (Ti1-xWxO2), named as Ir/Ti1-xWxO2. The continuous conductive chain could be formed by manipulating the catalyst synthesis conditions. To demonstrate the significance of the conductive chain in the electrochemical test, the Ir/Ti1-xWxO2 catalyst modified with an additional layer of IrO2, named as Ir/IrO2/Ti1-xWxO2, was prepared. Partial amount of iridium nanoparticles without conductive chain was oxidized to iridium oxide, and subsequently, another layer of iridium nanoparticles was deposited on the IrO2/Ti1-xWxO2 support to form an iridium/iridium oxide conductive chain. The electrochemical tests demonstrated that these two categories of catalysts with conductive chain exhibited high initial performance and durability for OER in PEM electrolyzers. The synthesized catalyst Ir/ WxTi1-xO2 demonstrated 5-time higher mass activity than industrial standard Ir black baseline, from rotating-disk electrodes (RDE) studies. While being tested in real water electrolyzers, the synthesized catalyst enabled to lower the Ir loading by an order of magnitude while retaining a similar electrolzyer performance of the baseline Ir black catalyst. The Ir/WxTi1-xO2 catalyst also demonstrated remarkable stability as only small voltage (<20 mV) increase was observed in a 3000-hour durability at a constant current density of 2000 mA/cm2.