Characterization Of Catalysts Research Articles

Role of Cr-doped NiO in reduction under a low concentration of H2 and CO

Nickel-chromium alloys are often utilized in high-resistance and heating metamaterials because of their passivity; however, their reducibility behavior has never been reported. Herein, Ni-Cr reduction has been conducted in H2 and CO atmospheres. Nickel oxide (NiO) catalysts were impregnated with chromium and subsequently subjected to temperature-programmed reduction (TPR) at low concentrations of CO and H2 to determine their reduction performance. The TPR profile fitting using a Gaussian function indicated the Cr-NiO reduction transformation of Cr6+→Cr3+ at temperatures below ∼300 °C for both reductant gasses. Furthermore, the addition of Cr shifted the reduction peaks to a lower temperature owing to the interaction of Cr and Ni atoms, leading to increased reducibility. The characterizations of the Cr-NiO catalyst using X-ray diffraction, Brunauer–Emmet–Teller surface area, scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS) analyses demonstrated the formation of NiCrxOy alloy with increasing surface area and porosity. The kinetic analysis using the Kissinger method demonstrated the reducibility of the catalysts with a low Ea value after the addition of Cr, where an Ea value of 68.0 kJ mol−1 (NiO) decreased to 49.3 kJ mol−1 (Cr-NiO) in the H2 atmosphere and an Ea value of 95.8 kJ mol−1 (NiO) decreased to 91.9 kJ mol−1 (Cr-NiO) in the CO atmosphere. The synergistic effects between Cr and Ni contributed to the increase in catalyst active sites by the transformation of the nickel oxidation state, which demonstrated the formation of oxygen vacancies and alloys, as proven via XPS analysis.

The role of Na for efficient CO2 hydrogenation to higher hydrocarbons over Fe-based catalysts under externally forced dynamic conditions

Considering the on-going developments of approaches for CO2 capture, storage, and utilization, CO2 hydrogenation with renewable H2 can become sustainable technology to produce value-added chemicals/fuels in future feedstock scenarios. Herein, we investigate temporal behaviors of Fe-based catalysts in CO2 hydrogenation under externally forced dynamics of reactor operation from the respective of composition and performance. Different catalyst preparation methods were applied to modulate the surface concentration of Na promoter but keeping the bulk concentration constant. The crucial promoter role in reserving catalyst performance and (un)steady-state catalyst composition during dynamic reactor operation was investigated by means of sophisticated catalytic tests combined with in situ and ex situ catalyst characterizations. The surface Na/Fe ratio of spent catalysts was identified as the decisive descriptor for production of the desired products under dynamic CO2 hydrogenation conditions. The derived knowledge could be useful for redesigning catalysts and optimizing reaction processes when employing fluctuating energy supply.

Structure-Property Relationships for Nickel Aluminate Catalysts in Polyethylene Hydrogenolysis with Low Methane Selectivity.

Earth-abundant metals have recently been demonstrated as cheap catalyst alternatives to scarce noble metals for polyethylene hydrogenolysis. However, high methane selectivities hinder industrial feasibility. Herein, we demonstrate that low-temperature ex-situ reduction (350 °C) of coprecipitated nickel aluminate catalysts yields a methane selectivity of <5% at moderate polymer deconstruction (25-45%). A reduction temperature up to 550 °C increases the methane selectivity nearly sevenfold. Catalyst characterization (XRD, XAS, 27Al MAS NMR, H2 TPR, XPS, and CO-IR) elucidates the complex process of Ni nanoparticle formation, and air-free XPS directly after reaction reveals tetrahedrally coordinated Ni2+ cations promote methane production. Metallic and the specific cationic Ni appear responsible for hydrogenolysis of internal and terminal C-C scissions, respectively. A structure-methane selectivity relationship is discovered to guide the design of Ni-based catalysts with low methane generation. It paves the way for discovering other structure-property relations in plastics hydrogenolysis. These catalysts are also effective for polypropylene hydrogenolysis.

Towards Machine Learning in Heterogeneous Catalysis-A Case Study of 2,4-Dinitrotoluene Hydrogenation.

Utilization of multivariate data analysis in catalysis research has extraordinary importance. The aim of the MIRA21 (MIskolc RAnking 21) model is to characterize heterogeneous catalysts with bias-free quantifiable data from 15 different variables to standardize catalyst characterization and provide an easy tool to compare, rank, and classify catalysts. The present work introduces and mathematically validates the MIRA21 model by identifying fundamentals affecting catalyst comparison and provides support for catalyst design. Literature data of 2,4-dinitrotoluene hydrogenation catalysts for toluene diamine synthesis were analyzed by using the descriptor system of MIRA21. In this study, exploratory data analysis (EDA) has been used to understand the relationships between individual variables such as catalyst performance, reaction conditions, catalyst compositions, and sustainable parameters. The results will be applicable in catalyst design, and using machine learning tools will also be possible.

In Situ Techniques for Characterization of Layered Double Hydroxide-Based Oxygen Evolution Catalysts

Functional layered double hydroxide (LDH) usually contains different cationic substitutes to increase the activity of the oxygen evolution reaction (OER). The intrinsic OER activity of LDH materials is connected with the chemical composition and dispersion of metal cations substitutions in the matrix phase. The potential induced phase transitions, in particular hydroxide-to-oxyhydroxide transitions, are a predisposition for the high OER activity of LDH materials and can be followed by coupling the electrochemical experiments with spectroscopic techniques. The understanding of LDH catalysts under electrochemical conditions also allows an understanding of the behavior of OER catalysts based on transition metals, metal-chalcogenides, -pnictides, -carbides, and metal–organic frameworks. The surfaces of those materials are intrinsically poor OER catalysts. However, they act as precursors to catalysts, which are oxidized into a metal (oxy)hydroxide. This review summarizes the use of in situ techniques for the characterization of LDH-based OER electrocatalysts and presents the influence of these techniques on the understanding of potential induced phase transitions, identification of active sites, and reaction mechanisms.

Upgrading of esterified bio-oil from waste coffee grounds over MgNiMo/activated charcoal in supercritical ethanol

In this work, the effect of reaction parameters such as temperature (250–375 °C), holding time (0–4 h), and bio-oil concentration (0–100 wt%) was investigated on upgrading of esterified CG-BO (CG-EBO) over MgNiMo/AC in supercritical ethanol. The esterification of CG-BO was conducted as a pretreatment to minimize the esterification reaction during the catalytic upgrading in supercritical ethanol. The MgNiMo/AC catalyst was found to play two crucial roles in the supercritical upgrading of CG-EBO; firstly, it facilitated hydrogen production through the dissociation of ethanol. Secondly, it enables the hydrodeoxygenation (HDO) reactions of CG-EBO by utilizing the hydrogen generated in situ. The biofuel products obtained by the supercritical upgrading were characterized by GC–MS, FT-IR, TAN, and elemental analyses. The catalyst characterization was accomplished by SEM-EDX, XRD, BET, N2-physiosorption Isotherms, H2-TPR, and TG analyses. Optimized conditions at 375 °C, 2 h holding time, and 20 wt% CG-EBO concentration were suggested for supercritical ethanol upgrading of CG-EBO over MgNiMo catalyst. A biofuel product with 48.6 wt% yield, 44.2 mg KOH/g TAN, and 4.0 wt% oxygen content (0.07 O/C) was obtained under the conditions. Simplified reaction pathways are suggested for supercritical ethanol upgrading of CG-EBO based on the products identified.

Synthesis of waste eggshell-derived Au/Co/Zn/eggshell nanocomposites for efficient hydrogen production from NaBH4 methanolysis

Developing new pathways to transform biological wastes into value-added products is inevitable in order to mitigate environmental pollution and providing sustainability. Utilisation of eggshell as a substrate, a naturally abandoned organic-inorganic waste, was explored in this study. Herein, Au/Co/Zn/eggshell nanocomposites were synthesised by utilizing waste eggshell as substrate. At the experimental stage, different metal combinations namely unary, binary and ternary combination of Co, Zn and Au and different ratios ranges from %10 to %50 were tested. The catalytic activity of the synthesised materials were investigated in terms of hydrogen production from NaBH4 methanolysis. The catalyst fabricated with the addition of %40 Co + %40 Zn + 3 ppm Au showed the best catalytic activity and the reaction completion time was as low as 2.4 min. The results revealed that the fabricated catalyst showed a superior catalytic activity with the maximum hydrogen production rate of 4394.6 mL/min/gcat. The obtained maximum hydrogen production rate is highly compatible with the existing literature. Different NaBH4 concentrations and catalyst concentrations were also tested to investigate the fabricated catalyst behaviour. The fabricated catalyst was also experimented in different temperatures range from 30 °C to 60 °C to determine the Arrhenius kinetics and subsequently activation energy. The activation energy was calculated to be 13.25 kJ/mol. SEM-EDX, BET, XRD and FT-IR analysis were finally performed to determine morphological and structural characterization of the superior catalyst.

Synthesis of mono, bi, and trimetallic Sn–Ni–Cu based ionic micro-emulsion catalysts and optimization of catalytic performance in heavy oil upgrading

In this study, to synthesize an active and feasible mono, bi, and trimetallic Sn–Ni–Cu/ionic microemulsion catalysts (IMECs), a novel synthesis process was proposed. All synthesized catalytic solutions and IMECs were characterized using conductivity, refractivity index (RI), inductively coupled plasma (ICP) and light microscope, physical stability, and Fourier transformed infrared spectroscopy (FTIR), respectively. Then, the interaction of catalyst formulation with operational parameters on the upgrading was experimentally evaluated. Statistical modeling was performed using the mixture-process algorithm of Design of Experiments (DOE). Experimental results and catalysts characterization specially FTIR outcomes reveal that shifting NO3−peaks of the trimetallic IMEC confirms the suitable preparation of IMEC. Moreover, trimetallic IMEC formulation of 23.09% Sn, 60.648% Ni, and 16.268% Cu which shows viscosity and produced gas weight percent (PGWP) of 586.99 cP and 1.269%, respectively, is the optimum catalyst formulation. Reaction temperature and catalysts wt% of 73 °C and 0.2% can be considered as the optimum operational condition. Finally, at 70 °C, increasing the amount of catalysts causes an increase in the speed of heavy to middle hydrocarbon reactions with reducing the effect of the mass transfer controlling mechanism. On the other hand, the reaction controlling mechanism for the production of light hydrocarbon from heavy oil was eliminated by changing the reaction temperature from 70 to 90 °C.

Sustainable syngas production by oxy-steam reforming of simulated biogas over NiCe/MgAl hydrotalcite-derived catalysts: Role of support preparation methods on activity

Herein, a series of hydrotalcite-derived MgAl supports were prepared by co-precipitation and hydrothermal methods. NiCe/MgAl catalysts were prepared by loading Ni (10 wt%) and Ce (2.5 wt%) on supports using sequential incipient wetness impregnation and tested in oxy-steam reforming of simulated biogas to produce syngas. N2-physisorption, XRD, XPS, SEM, TEM, ICP-OES, TGA, and Raman were used for catalyst characterization. Reactivity was evaluated at 600 °C, 700 °C, and 800 °C with a constant GHSV (45,000 ml gcat−1 h−1) and feed ratio (CH4/CO2/O2/H2O = 1/0.67/0.1/0.3). The results demonstrate that increasing the co-precipitation aging temperature and the hydrothermal reaction temperature affected the surface area, pore volume, and Ni crystallite size. However, no significant change in reactivity was observed. The NiCe/MgAl catalyst with co-precipitation aging temperature of 140 °C (NCMA140-Co) exhibited lower carbon deposition probably due to higher Ce4+ concentration. Therefore, NCMA140-Co provided high stability and conversions of CH4 (94%) and CO2 (82%) with H2/CO ratio (1.6) at 800 °C without carbon deposition.

Synthesis and Characterisation of Calcium Oxide Catalyst Derived from Waste Oyster Shells for Transesterification of Glycerol

Synthesis and Characterisation of Calcium Oxide Catalyst Derived from Waste Oyster Shells for Transesterification of Glycerol

Effective removal of azithromycin by novel g-C3N4/CdS/CuFe2O4 nanocomposite under visible light irradiation

In this study, the visible light active pristine, binary and ternary g-C3N4/CdS/CuFe2O4 nanocomposite is prepared through a coprecipitation-assisted hydrothermal technique. The characterization of the as-synthesized catalysts was conducted using various analytical techniques. When compared with pristine and binary nanocomposites, the ternary g-C3N4/CdS/CuFe2O4 nanocomposite exhibits higher photocatalytic degradation of azithromycin (AZ) under a visible light source. Ternary nanocomposite exhibits high AZ removal efficiency of about 85% within 90 min of the photocatalytic degradation experiment. Enhanced the visible light absorption ability and the suppression of photoexcited charge carriers is also achieved by forming heterojunctions between pristine materials. The ternary nanocomposite exhibited ∼2 times higher degradation efficiency than CdS/CuFe2O4 nanoparticles and ∼3 times higher degradation efficiency than CuFe2O4. The trapping experiments were conducted and it shows superoxide radicals (O2•-) are the predominant reactive species involved in the photocatalytic degradation reaction. This study provided a promising approach for the treatment of contaminated water using g-C3N4/CdS/CuFe2O4 as a photocatalyst.

Synthesis and characterization of SO3H-functionalized silica solid acid catalyst and application for the production of diosgenin

Synthesis and characterization of SO3H-functionalized silica solid acid catalyst and application for the production of diosgenin

Rapid and complete inactivation of pathogenic microorganisms by solar-assisted in-situ H2O2 generation using a polypyrrole-supported copper sulfide system

In this study, we report a photo-assisted H2O2 self-supply and in-situ activation system based on the polypyrrole-supported copper sulfide (solar/Cu2−xS@PPy) for water disinfection. 6.57-log, 4.22-log, and 5.23-log inactivation of Escherichia coli K-12 (even at a viable but nonculturable state), Bacillus subtilis spores, and bacteriophage MS2 are achieved within 60 min by using the solar/Cu2−xS@PPy system in batch and flow-through reactors. Catalyst characterization and theoretical calculation results suggest that the photo-generated H2O2 is in-situ activated by the Cu−N bridges in Cu2−xS@PPy·H2O2 is oxidized to •O2- and ultimately 1O2 on Cu sites, and electrons are subsequently pumped to electron-rich N sites (H2O2→Cu→N) to maintain the balance of electron donation-acquisition. The electrons can be directly extracted from cell membranes to Cu2−xS@PPy, making cells vulnerable to reactive oxygen species and heat. This work provides a novel and affordable solution for the rapid disinfection of drinking water in rural and underdeveloped areas.

Dual Atom Catalysts for Energy and Environmental Applications.

The pursuit of high metal utilization in heterogeneous catalysis has triggered the burgeoning interest of various atomically dispersed catalysts. Our aim in this review is to assess key recent findings in the synthesis, characterization, structure-property relationship and computational studies of dual-atom catalysts (DACs), which cover the full spectrum of applications in thermocatalysis, electrocatalysis and photocatalysis. In particular, combination of qualitative and quantitative characterization with cooperation with DFT insights, synergies and superiorities of DACs compare to counterparts, high-throughput catalyst exploration and screening with machine-learning algorithms are highlighted. Undoubtably, it would be wise to expect more fascinating developments in the field of DACs as tunable catalysts.

Boosting the Photocatalysis of Plasmonic Au-Cu Nanocatalyst by AuCu-TiO2 Interface Derived from O2 Plasma Treatment.

Plasmonic gold (Au) and Au-based nanocatalysts have received significant attention over the past few decades due to their unique visible light (VL) photocatalytic features for a wide variety of chemical reactions in the fields of environmental protection. However, improving their VL photocatalytic activity via a rational design is prevalently regarded as a grand challenge. Herein we boosted the VL photocatalysis of the TiO2-supported Au-Cu nanocatalyst by applying O2 plasma to treat this bimetallic plasmonic nanocatalyst. We found that O2 plasma treatment led to a strong interaction between the Au and Cu species compared with conventional calcination treatment. This interaction controlled the size of plasmonic metallic nanoparticles and also contributed to the construction of AuCu-TiO2 interfacial sites by forming AuCu alloy nanoparticles, which, thus, enabled the plasmonic Au-Cu nanocatalyst to reduce the Schottky barrier height and create numbers of highly active interfacial sites. The catalyst's characterizations and density functional theory (DFT) calculations demonstrated that boosted VL photocatalytic activity over O2 plasma treated Au-Cu/TiO2 nanocatalyst arose from the favorable transfer of hot electrons and a low barrier for the reaction between CO and O with the construction of large numbers of AuCu-TiO2 interfacial sites. This work provides an efficient approach for the rational design and development of highly active plasmonic Au and Au-based nanocatalysts and deepens our understanding of their role in VL photocatalytic reactions.

Investigation on deactivation progress of biochar supported Ni catalyst during biomass catalytic cracking process

Herein, the biochar-supported Ni catalysts was synthesized by carbothermal reduction and its catalytic activity for biomass-derived heavy components was investigated in a pyrolysis-catalysis two stage reactor at the catalytic cracking temperature of 700 °C. The change in catalytic activity of biochar-supported Ni catalyst was divided into three stages according to conversion efficiency of heavy components: rapid reduction stage (from 95.30% to 85.58%), stabilization stage (from 84.65% to 82.98%), and slow reduction stage of activity (from 81.21% to 76.98%), corresponding to rapid decreasing stage (from 88.95% to 63.53%), stable stage (from 62.1% to 57.55%), and slow increasing stage (57.66% to 60.17%) of the mass retention percentage of catalyst. The characterizations of catalyst after different cycles showed that the initial deactivation mainly caused by the sintering of Ni active sites. With the severe sintering of Ni nanoparticles, coke deposition became the main reason of later catalyst deactivation. Particularly, the carbon elimination reaction promoted by highly dispersed Ni particle was observed which contributed to enrich the mesoporous structure and retarded the deactivation of the catalyst. The research marks a further understanding of the interaction and deactivation mechanisms between biochar support and Ni active sites during catalytic cracking of biomass-derived heavy components.

Synthesis of Vinyl Acetate Monomer Over PdCu Alloys: The Role of Surface Oxygenation in the Reaction Path

AbstractThis work uses sol–gel and sonochemical methods to prepare bimetallic PdCu catalysts supported on modified ZrO2 with Ti and Al. The catalysts are tested for vinyl acetate synthesis from ethylene, acetic acid, and oxygen, varying the reaction temperature for two catalysts prepared, which show higher activity. Catalysts characterization results show bimetallic species and distort alloys with a dispersed distribution of active metal onto the support. The in situ reaction by DRIFT‐MS identifies the surface formation of main intermediates like palladium acetate monomers and mono and bidentate intermediates, associated to vinyl acetate formation, like vinyl hydrogenated species over PdCu. Finally, this behavior will be attributed to the bimetallic distortions of PdCu samples, provided by interaction effects between PdCu and supports, indicating a more exposition of PdCu species suitable for the reaction, according to high‐resolution transmission microscopy electron microscopy results for PdCu/ZrTi sample. Thus, this sample exhibits a minimal formation of sub‐products and catalytic stability for 18 hh. These results evidence the participation of hydroxyls and oxygen vacancies of the catalyst in the catalytic reaction measured in situ, monitoring the products formed at the reactor outlet. Finally, it is proposed a reaction pathway as a function of reaction conditions.

Optimizing hollow ZSM-5 spheres (hZSM5) morphology and its intrinsic acidity for hydrogenation of CO2 to DME with copper–aluminum

Hollow zeolites are normally made by synthesizing parent rigid zeolites form soluble silica-alumina suspension followed by removal of the aluminum-deficient centers, during which the uniformity of hollow zeolites is compromised. Herein, two uniform spherical hollow ZSM-5 (hZSM5) with distinct morphologies, monodispersed (mhZSM5) and networked (nhZSM5), were hydrothermally synthesized using premade Stöber SiO2 spheres along with structure directing agents with and without aluminum. Subsequently, both mhZSM5 and nhZSM5 supports were impregnated with mono- and multimetallic Cu-based catalysts to investigate CO2 hydrogenation with in-depth catalyst characterizations (HRTEM-EDX, Pyridine-FTIR, H2-TPR, XPS, XANES, and DRIFTS). It was evidenced that uniform and decent morphology of mhZSM5 spheres arises from the existence of framework-intrinsic Al3+. Besides, it was revealed that mhZSM5-AlCu containing both framework-intrinsic Al3+ and catalyst-extrinsic Al3+ promoter leads to an optimal DME production (33.5 mgDME·gcat.−1·h−1), which is comparable or even higher to the ones reported in several published works. Not only was mhZSM5-AlCu activity even better, but also it showed a prolonged stability compared to comZSM5-AlCu and nsZSM5-AlCu samples that were derived using commercial ZSM-5 supports with better physiochemical properties. Based on our in-situ DRIFTS, a step-wise mechanistic pathway of DME formation over mhZSM5-AlCu was proposed, assuming that the hollow ZSM-5 shell framework dehydrates methanol that is formed in-situ via CO2 hydrogenation.

Low-Temperature Water Gas Shift Reaction over Highly Dispersed Ir on TiO2─Influence of the Ir Dispersed State and the Metal–Support Interface

Oxide-supported iridium (Ir) metal catalysts exhibit superior activity for the low-temperature water gas shift (WGS) reaction. In this study, highly dispersed Ir supported on anatase TiO2 shows a relatively high turnover frequency and a relatively low activation energy for the WGS reaction compared to that reported in the literature. Catalyst characterization reveals the presence of small clusters and single atoms (SAs). Density functional theory (DFT) calculations show that the WGS reaction proceeds preferentially via a carboxyl mechanism with carboxyl formation as the rate-determining step on both TiO2-supported Ir clusters and SAs, which can be supported by experimental observations. In situ diffuse reflectance infrared Fourier transform spectroscopy, corroborated by DFT calculations, indicates that CO co-adsorbed with H2O at the interface between the Ir cluster and TiO2 plays the key role in low-temperature WGS starting from room temperature. DFT calculations show that the energy barrier of carboxyl formation over the Ir cluster is lower than that over Ir SAs, indicating that the Ir clusters may have contributed more to the low-temperature WGS activity. The excellent catalytic activity of the Ir/a-TiO2 catalyst reveals its potential application for low-temperature WGS.

Facilitating electroreduction CO2-to-C2H4 over doped CuO nanospheres assisted by nitrogen species and oxygen vacancies

Electrocatalytic reduction is a promising strategy for CO2 utilization, while the conversion of CO2 to C2 products usually suffers from the low selectivity. Herein, we report several high-performance Cu-OCN catalysts for electroreduction CO2-to-C2H4, which are prepared through the in-situ calcination of nanocube Cu2O and urea. The highest C2H4 faradaic efficiency from Cu-OCN-10 reaches 55.97%, much higher than that from the pristine CuO counterpart (38.31%), with a partial current density of −12.83 mA cm−2. Catalyst characterizations and first-principles density functional theory calculations reveal that the superior performance of CuO-OCN is attributed to the introduced nitrogen (N) species and oxygen (O)-vacancies. With the assistance of N species and O-vacancies, the adsorption of CO2 on Cu-OCN-10 is thermodynamically favorable with the absorption energy of −0.69 eV. Meanwhile, the activation of CO2 is promoted and the generated *CO intermediate on Cu-OCN-10 is stable, whose release needs to overcome an energy of 2.26 eV, thereby enhancing the CC coupling to produce C2H4. In general, the synergistic effects of N species and O-vacancies in Cu-OCN catalysts facilitate CO2 electroreduction to C2H4.