Catalyst Preparation Procedure Research Articles

Syntheses, catalytic performances and DFT investigations: A recent review of copper-based catalysts of methanol steam reforming for hydrogen production

Copper-based catalysts have demonstrated notable efficacy in facilitating methanol conversion and hydrogen yield at low temperatures. Given the straightforward and cost-effective nature of the process, further investigation into this area is merited. This article provides a summary of the progress made in the development of copper-based catalysts for hydrogen production through methanol steam reforming. The catalytic performance of conventional Cu/ZnO/Al2O3 catalysts can be exceeded by utilizing specific catalyst formulations and preparation procedures, which are characterized by their intricate structural and chemical properties. The studies about MSR mechanism have also been integrated. The realm of DFT research encompasses an examination of the monatomic systems, which have garnered significant attention in contemporary times. Furthermore, this paper presented potential avenues for future research on copper-based catalysts in the context of MSR. We believe that the forthcoming research will concentrate on the design, preparation, and molecular mechanism of copper-based catalysts that exhibit high stability, high activity, and low CO selectivity.

5Ni/MgO and 5Ni/MgO + MOx (M = Zr, Ti, Al) Catalyst for Hydrogen Production via Dry Reforming of Methane: Promotor-Free, Cost-Effective, and Handy Catalyst System

Utilization of CO2 as a promising oxidant under dry reforming methane (DRM) can mitigate two greenhouse gases (CO2 and CH4) together, as well as DRM reaction may be a source of H2 energy in future. The cost-effective and handy catalyst preparation procedures like mixing, drying and calcining may turn this reaction from lab to industry. In this line, herein, 5Ni/MgO and 5Ni/MgO + MOx (M = Zr, Ti, Al) catalysts were prepared, investigated for DRM and characterized by X-ray diffraction, Raman, temperature programmed reduction/desorption, thermogravimetry and transmission electron microscope. Among the prepared catalysts, the 5Ni/MgO + TiO2 catalyst exhibits the highest concentration of active Ni sites enhanced reducibility under oxidizing and reducing environments, but catalytic excellency is hindered by severe graphitic-type coke deposition. On the other hand, the 5Ni/MgO + Al2O3 catalyst predominantly comprises metallic Ni resulting from the reduction of “strongly interacted NiO”, expanded surface area and the highest concentration of easily accessible active sites, contributing to its superior performance (H2 yield ~ 71% up to 430 min time on stream) under oxidizing and reducing conditions during DRM. The outstanding performance of the 5Ni/MgO + Al2O3 catalyst marks a significant stride towards the development of an industrially viable, cost-effective, and convenient catalyst system for DRM.Graphical

Liquid-Phase Partial Hydrogenation of Phenylacetylene at Ambient Conditions Catalyzed by Pd-Fe-O Nanoparticles Supported on Silica.

Catalysts with no hazardous or toxic components are required for the selective hydrogenation of acetylenic bonds in the synthesis of pharmaceuticals, vitamins, nutraceuticals, and fragrances. The present work demonstrates that a high selectivity to alkene can be reached over a Pd-Fe-O/SiO2 system prepared by the co-impregnation of a silica support with a solution of the metal precursors (NH4)3[Fe(C2O4)3] and [Pd(NH3)4]Cl2 followed by thermal treatment in hydrogen or in air at 400 °C. A DRIFT spectroscopic study of CO adsorption revealed large shifts in the position of the Pdn+-CO bands for this system, indicating the strong effect of Fen+ on the Pd electronic state, resulting in a decreased rate of double C=C bond hydrogenation and an increased selectivity of alkyne hydrogenation to alkene. The prepared catalysts consisted of mono- and bimetallic nanoparticles on an SiO2 carrier and exhibited a selectivity as high as that of the commonly used Lindlar catalyst (which contains such hazardous components as lead and barium), while the activity of the Fe-Pd-O/SiO2 catalyst was an order of magnitude higher. The hydrogenation of a triple bond over the proposed Pd-Fe catalyst opens the way to selective hydrogenation over nontoxic catalysts with a high yield and productivity. Taking into account a simple procedure of catalyst preparation, this direction provides a rationale for the large-scale implementation of these catalysts.

Uniform Si‐Infused UiO‐66 as a Robust Catalyst Host for Efficient CO2 Hydrogenation to Methanol

AbstractDue to the weak nature of organic coordination bonds, metal–organic frameworks (MOFs) can hardly retain their intrinsic physicochemical properties and structural integrity when functioning in harsh heterogeneous reactions. Herein, a post‐synthetic strategy to reinforce the MOF structure by inserting siliceous linkers inside is proposed, according to which a Si‐infused UiO‐66 (s‐UiO‐66) with well‐developed porosity and exceptional thermal/structural stability is fabricated. This monodispersed Si‐infused matrix with enlarged nanopores is then utilized as the catalyst host, and is highly conductive to confining ultrafine CuO nanoparticles with uniform dispersion. Targeting CO2 hydrogenation to methanol reaction, the Cu‐loaded s‐UiO‐66 (CuO/s‐UiO‐66) delivers a remarkable and efficient methanol production rate outperforming other Cu/ZrO2‐based catalysts and the commercial catalyst. Moreover, the robust structure of CuO/s‐UiO‐66 prevents both copper phase and host material from aggregation during the catalyst preparation procedure and the reaction. In addition to material‐oriented studies, in situ characterization techniques are employed to identify the active Cu component and key intermediates formed during the CO2 hydrogenation reaction, separately. It is envisioned that this Si infusion strategy can be applied to construct stable host materials with boundary‐defined structures from the pristine MOFs for broadened applications under extreme circumstances.

Nanocomposite catalysts of non-purified MoVNbTeOx with CeO2 or TiO2 for oxidative dehydrogenation of ethane

The phase-pure M1 of MoVNbTeOx has been demonstrated as a highly active catalyst for oxidative dehydrogenation of ethane (ODHE) reaction. However, the MoVNbTeOx without further purification shows poor catalytic performance so that the M2 phase has to be removed from the bulk material to approach the high purity of M1 phase. This work presents new discovery that the nanocomposite catalyst by adding CeO2 to the MoVNbTeOx using sol–gel method can effectively promote its catalytic performance. As a comparison, the sample combining TiO2 and MoVNbTeOx is also prepared which presents limited influence. The characterization results show that the enhanced catalyst performance can be attributed to the increased active species at the catalyst surface due to the addition of CeO2. This work would provide a new solution to greatly simplify the preparation procedure of MoVNbTeOx catalysts for the ODHE process and avoid the mass loss during the purification procedure.

Copper mesh supported nickel nanowire array as a catalyst for the hydrogen evolution reaction in high current density water electrolysis.

Hydrogen generation by water splitting using various renewable energy sources will play an important role in the sustainable green energy supply of the future. Unfortunately, wide industrial adoption of this process is currently impeded by the necessity to use noble metal based electrolysis catalysts. In this study, a low-cost and highly efficient water electrolysis catalyst active in the hydrogen evolution reaction (HER) taking place in alkaline medium is developed. The catalyst preparation procedure consists of electrodeposition of a rough nickel layer onto a smooth copper mesh, followed by the growth of hierarchical Ni nanowires on its surface. The rough nickel layer provides plenty of active sites for nanowire formation, resulting in a synergetic effect between copper and nickel in the copper mesh supported nickel nanowire array, which effectively enhances the HER electrocatalytic performance of this novel material. The catalyst demonstrated an HER overpotential as low as 317 mV in 1 M KOH electrolyte at a current density of 1 A cm-2. The copper substrate's superior electrical conductivity to that of nickel is responsible for the excellent HER performance of the catalyst at high current density, making it a promising candidate to replace highly expensive noble metal based electrodes.

CO2 Methanation: Nickel-Alumina Catalyst Prepared by Solid-State Combustion.

The development of solvent-free methods for the synthesis of catalysts is one of the main tasks of green chemistry. A nickel–alumina catalyst for CO2 methanation was synthesized by solid-state combustion method using hexakis-(imidazole) nickel (II) nitrate complex. Using X-ray Powder Diffraction (XRD), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Hydrogen temperature-programmed reduction (H2-TPR), it was shown that the synthesized catalyst is characterized by the localization of easily reduced nickel oxide on alumina surface. This provided low-temperature activation of the catalyst in the reaction mixture containing 4 vol% CO2. In addition, the synthesized catalyst had higher activity in low-temperature CO2 methanation compared to industrial NIAP-07-01 catalyst, which contained almost three times more hard-to-reduce nickel–aluminum spinel. Thus, the proposed approaches to the synthesis and activation of the catalyst make it possible to simplify the catalyst preparation procedure and to abandon the use of solvents, which must be disposed of later on.

Preparation of highly effective carbon black supported Pd–Pt bimetallic catalysts for nitrobenzene hydrogenation

Carbon black (CB) supported palladium–platinum catalysts were prepared with and without nickel(II) oxide or iron(III) oxide promoter materials. By applying ultrasonic cavitation highly efficient CB supported catalysts were created. The designed catalyst preparation is a one-step procedure, as post-treatments (e.g. calcination, hydrogen activation) are not necessary. The activation of the catalysts occurs during their preparation due to the ultrasonic cavitation. Thus, a fast and simple catalyst preparation procedure have been developed. The activity of the catalysts was compared in nitrobenzene hydrogenation at different temperatures in the range of 283–323 K at 20 bar hydrogen pressure. In terms of selectivity and aniline yield, no significant differences were detected even when promoters were present. By using the NiO promoter, the activation energy was extremely low (7.6 ± 0.7 kJ mol−1). The selectivity was over 99% in every case, and 99.6% aniline yield was achieved without any promoters (99.7% with NiO), while less than 1.0% by-products were formed. The reaction rate was high with every catalyst, and no significant differences were detected. All in all, the prepared catalysts show excellent catalytic activity in the hydrogenation of nitrobenzene.

Biodiesel production catalyzed by NaOH/Magnetized ZIF-8: Yield improvement using methanolysis and catalyst reusability enhancement

The current study investigates the methanolysis reaction to increase biodiesel yield using the recently developed NaOH/magnetized ZIF-8 catalyst. The effects of methanol to oil ratio and catalyst dose on oil conversion with their interaction were studied by employing full factorial design and response surface methodology. Two-factor interaction model was selected as the best model to fit the experimental data with a determination coefficient (R2) of 0.97 where all the model’s parameters were significant. The two factors were found positively influencing the reaction conversion. The maximum observed conversion reached almost 100% at 21:1 M methanol to oil ratio and 3 wt% catalyst/oil ratio. Additionally, the kinetic study revealed that pseudo-second order kinetic model fits the experimental data well. In addition, the Arrhenius equation analysis showed lower activation energy and higher pre-exponential factor for methanolysis in comparison with ethanolysis indicating the faster kinetics. Besides, ASTM standard testing techniques confirmed that the produced esters at optimum conditions can be used as biodiesel sustainable fuel. Finally, several modifications in the catalyst preparation conditions or procedure showed their ability to increase catalyst stability and reusability characteristics.

Interfacial coordination chemistry for catalyst preparation

The concept of interfacial coordination chemistry was one of the innovation for which Michel Che became internationally known during his tenure as full professor at the Université Pierre et Marie Curie. Isolated metal ions on oxide surfaces behave like coordination compounds to which the surface contributes not only via neutral oxo bridges but also via hydroxyl groups. The latter being pH sensitive, the surface can be charged either positively or negatively, allowing selective adsorption of transition metal ions of opposite charge. In the early eighties, examples exploiting these properties for the preparation of oxide/metal supported catalysts were still rare. This review presents Michel Che’s early studies, mostly on molybdenum and nickel ions, on which he built, developed and promoted the concept of interfacial coordination chemistry, now widely used in the field of heterogeneous catalysis. This allowed him and his close collaborators to achieve a molecular-scale understanding of several catalyst preparation procedures, such as impregnation, selective adsorption, grafting, deposition–precipitation, and zeolite functionalization. The impact and legacy of the concept of Interfacial Coordination Chemistry on the current design of improved catalytic formulations is also reviewed.

Mechanistic in situ investigation of heterogeneous hydrogenation over Rh/TiO2 catalysts: selectivity, pairwise route and catalyst nature.

The selectivity of product formation is strongly correlated with the nature of the catalyst active centers. Therefore, the selective synthesis of active sites with certain structure is a big challenge in modern catalysis. Here synthetic procedures are adopted for the formation of 1% Rh/TiO2 catalysts with different properties. It is shown that the nature of the precursor used for catalyst preparation is important, and that the use of a solution of rhodium acetate instead of rhodium nitrate leads to the selective formation of butenes during 1,3-butadiene hydrogenation. The use of parahydrogen in the reaction results in the enhancement of NMR signals via parahydrogen-induced polarization (PHIP) for all synthesized catalysts, and this signal enhancement increases with increasing catalyst calcination temperature. This effect is explained by the decoration of rhodium nanoparticles with titania which restricts hydrogen mobility on the surface, leading to the highest reported to date selectivity toward the pairwise hydrogen addition route of 7% for supported metal catalysts.

One-pot hydrothermal synthesis of a novel Pt@CeO2 nanocomposite for water-gas shift reaction

A Pt-doped ceria nanocomposite with controlled morphology was prepared by one-pot hydrothermal synthesis method. The crystalline structure, texture and metal dispersion of the novel Pt@CeO2 sample were studied by powder XRD, TEM, XPS, H2-TPR, N2-adsorption and CO chemisorption. The catalyst preparation procedure under hydrothermal conditions had significant impact on the Pt nanoparticles growth rate. Highly dispersed Pt species can be sufficiently anchored on the surface of nanopolyhedral CeO2. The nanopolyhedral Pt@CeO2 catalyst exhibits excellent catalytic activity for the water-gas shift reaction, suggesting an intimate interaction between Pt nanoparticles and nanopolyhedral CeO2 that promotes the generation of additional active sites.

CO2 Hydrogenation to Methanol with Ga- and Zn-Doped Mesoporous Cu/SiO2 Catalysts Prepared by the Aerosol-Assisted Sol-Gel Process*.

The preparation of copper-based heterogeneous catalysts dedicated to the hydrogenation of CO2 to methanol typically relies on multi-step procedures carried out in batch. These steps are precisely tailored to introduce the active phase (Cu) and the promoters (e. g., zinc, gallium) onto a preformed support to maximize catalyst performance. However, each process step can be associated with the formation of waste and with the consumption of energy, thereby negatively impacting the environmental performance of the overall catalyst preparation procedure. Here, a direct and continuous production process is proposed for the synthesis of efficient catalysts for the CO2 -to-methanol reaction. Gallium- and zinc-promoted mesoporous Cu-SiO2 catalysts were prepared in one step by the aerosol-assisted sol-gel process. The catalysts consisted of spherical microparticles and featured high specific surface area and pore volume, with interconnected pores of about 6 nm. A strong promoting effect of Ga and Zn was highlighted, boosting the selectivity for methanol at the expense of CO. Upon calcination, it was shown that Cu species (initially trapped in the silica matrix) underwent a migration towards the catalyst surface and a progressive sintering. After optimization, the catalysts obtained via such direct, continuous, simple, and scalable route could compete with the best catalysts reported in the literature and obtained via multi-step approaches.

N-formylation of amines using phenylsilane and CO2 over ZnO catalyst under mild condition

Several research studies have been conducted on N-formylation of amines using phenylsilane and CO2. However, most of these studies involved tedious processes of catalyst preparation or complex procedures. In the present study, we describe the use of a simple and commercially available ZnO catalyst for selective N-formylation of amines under mild condition. High-yielding N-formylation products with good recyclability and wide substrate scope were obtained, which can promote fine chemical synthesis and CO2 capture.

Effect of preparation procedure and composition of catalysts based on Mn and Ce oxides in the simultaneous removal of NOX and o-DCB

Two series of catalysts based on Mn and Ce oxides were prepared by co-precipitation and impregnation, in order to study their physicochemical properties and catalytic performance in the simultaneous reduction of NO and oxidation of o-DCB. Co-precipitation catalysts showed better activity than those prepared by impregnation because of the formation of a MnOX-CeO2 solid solution, which improves redox and acid properties. Moreover, the catalysts with MnOX content between 80 and 90 mol.%, in which a coexistence between solid solution phase and Mn2O3 crystal was found, presented NO conversion above 90 % at temperatures below 250 °C and o-DCB conversion above 80 % at temperatures above 200 °C. The main by-products of SCR were N2O, produced in the whole range of temperature, and NO2, formed at temperatures above 300 °C. Selectivity to CO2 above 80 % was obtained using co-precipitation catalysts in all temperature range. Deactivation experiments showed that oxidation reaction strongly contributes to deactivate impregnation catalysts, whereas the effect of deactivation is lower in co-precipitation catalysts at high Mn contents.

Gold-Containing Catalysts Based on Mesoporous Metal–Organic Frameworks of the MIL Type for Regioselective Hydroamination Reaction of Phenylacetylene

Catalyst systems based on gold nanoparticles introduced into the matrices of mesoporous metal–organic frameworks of the MIL type based on trivalent metal ions (Al, Fe) manifest activity in the regioselective hydroamination of phenylacetylene with aniline according to the Markovnikov rule. The activity of the synthesized gold-containing systems significantly depends on the nature of organic and inorganic building units, metal ions, and organic linkers, which form the framework, as well as on the catalyst preparation procedure.

K2WO4/Al2O3 catalysts for methanethiol synthesis from methanol and H2S: effect of catalyst preparation procedure

A series of the K2WO4/γ–Al2O3 catalysts was prepared with different introducing strategy of the K2WO4 to alumina and characterized by means of N2 adsorption–desorption, XRD, XPS, CO2/NH3-TPD, H2-TPR. It was found that the different introduction strategy of K2WO4 did not change the valence state of surface species of the catalysts but markedly influenced the structures, dispersion of tungsten and potassium species and acid-basic properties. The catalysts prepared by the sol–gel precipitation method exhibit larger surface area, better dispersion of the W species and more favorable acid-basic properties, thus possess higher activity for the reaction, particularly, at the lower reaction temperature of 320 °C, the methanethiol yield was about 8.3% higher than that over the catalyst prepared by traditional impregnation method. As a model catalyst, the catalysts prepared by sol–gel precipitation method show a higher and more stable reactivity with small dosage of water and CS2, and worth in industrial application.

Utilization of cacao peel waste to K2O heterogeneous catalyst in biodiesel synthesis by waste cooking oil: effect of catalyst calcination temperature

Calcination is one way to take advantage of K2O content of cocoa pods husks potential as a catalyst in the production of biodiesel. The purpose of this research is the utilization of waste pod husks as heterogeneous catalysts in the manufacture of biodiesel from waste cooking oil. The catalyst preparation procedure of the cocoa shell ash is waste cocoa husk first cleaned by washing, so free from impurities such as mud and other substances. The peel then cut into small pieces and dried in the sun for two weeks to reduce the water content of the cocoa peel and smoothed by using ballmill. In this study, an analysis that is proximate analysis such as the water content of the sample and the catalyst, volatile matter, ash content, yield of ash, fixed carbon, pH and also do analysis of the pore structure of the catalyst by using analysis of SEM-EDS analysis and potassium (K2O) with AAS analysis. The best conditions are obtained the purity of 99.58% with a methyl ester methyl ester yield of 92.68% with a mole ratio of alcohol and the use of used cooking oil 12: 1, a reaction temperature of 65 °C, the amount of catalyst is 6% (w / w) which are calcined at a temperature of 650 °C and reaction time of 180 minutes. The results of the present study indicate that the use of cocoa peel and used cooking oil is a catalyst and cheap raw materials suitable in the manufacture of biodiesel.

How Catalysts and Experimental Conditions Determine the Selective Hydroconversion of Furfural and 5-Hydroxymethylfurfural

Furfural and 5-hydroxymethylfurfural stand out as bridges connecting biomass raw materials to the biorefinery industry. Their reductive transformations by hydroconversion are key routes toward a wide variety of chemicals and biofuels, and heterogeneous catalysis plays a central role in these reactions. The catalyst efficiency highly depends on the nature of metals, supports, and additives, on the catalyst preparation procedure, and obviously on reaction conditions to which catalyst and reactants are exposed: solvent, pressure, and temperature. The present review focuses on the roles played by the catalyst at the molecular level in the hydroconversion of furfural and 5-hydroxymethylfurfural in the gas or liquid phases, including catalytic hydrogen transfer routes and electro/photoreduction, into oxygenates or hydrocarbons (e.g., furfuryl alcohol, 2,5-bis(hydroxymethyl)furan, cyclopentanone, 1,5-pentanediol, 2-methylfuran, 2,5-dimethylfuran, furan, furfuryl ethers, etc.). The mechanism of adsorption of the reactant and the mechanism of the reaction of hydroconversion are correlated to the specificities of each active metal, both noble (Pt, Pd, Ru, Au, Rh, and Ir) and non-noble (Ni, Cu, Co, Mo, and Fe), with an emphasis on the role of the support and of additives on catalytic performances (conversion, yield, and stability). The reusability of catalytic systems (deactivation mechanism, protection, and regeneration methods) is also discussed.

Carbon-Based Catalysts for Oxygen Reduction Prepared By Ball Milling

Carbon-based materials, for example graphite, graphene, graphene oxide (GO), have been widely used as substrates in various fields including electrocatalysis and electroanalysis. More specifically, nanocarbons have been considered as electrode materials including but not limited to (bio)fuel cells, supercapacitors and (bio)sensors. The main advantages of the electrodes based on carbon nanomaterials are their low cost compared to metals, mechanical stability and a wide potential window in electrochemistry.1 The oxygen reduction reaction (ORR), which takes place for example in fuel cells, metal-air batteries and (bio)sensors, greatly depends on the electrode material. Therefore, a major focus is on the development of efficient cathode catalysts for the ORR. It is well-known that the reduction of oxygen is rather inhibited on pristine carbon materials.2,3 However, a range of carbon-based materials like heteroatom-doped carbon or transition metal-nitrogen-carbon have shown great promise as ORR electrocatalysts in alkaline media.1,2 Up to date, in most cases, complicated synthesis procedures have been employed to produce the ORR catalysts. Therefore, on the one hand, it is very important to develop a catalyst with high ORR activity. But on the other hand, it is crucial to use a simple but efficient approach for the preparation of good ORR catalyst. In this regard, ball milling has been usually used to reduce the size of the carbon material, but ball milling has also been employed in order to modify the surface of the nanocarbon.4,5 These advantages make ball milling an attractive method to produce catalysts for the ORR. In this study, a very simple method based on ball milling is employed in order to synthesize ORR catalysts. In more specific, transition metal and nitrogen co-doped or solely nitrogen-doped nanocarbon catalysts were synthesized by ball milling using different carbon materials in the presence of metal-nitrogen or nitrogen precursor followed by pyrolysis at 800 °C. For the physico-chemical characterization of the doped carbon-based catalysts, scanning electron microscopy, energy dispersive X-ray spectroscopic measurements and X-ray photoelectron spectroscopy were used. The SEM images revealed different morphology for the catalysts. In addition, the elemental analysis of the materials showed that depending on the catalyst preparation procedure, metal and nitrogen or only nitrogen was detected in the catalyst material. The electrochemical measurements in O2-saturated 0.1 M KOH conducted by the rotating disk electrode method exhibited good electrocatalytic activity of all of these catalysts toward the ORR compared to the unmodified carbon materials. This shows that the simple method based on ball milling proposed herein is suitable for the synthesizing ORR catalysts.