Multifunctional Catalyst Systems Research Articles

Multifunctional core@shell structured gold nanodendrites@gold nanoclusters: An efficient catalytic and sensor domain for environmental remediation applications

Over the recent decades, rapid industrialization, the excess use of chemical reagents, and their improper waste disposal to the environment caused severe damage to the ecosystem. To get rid of these serious issues, the propitious solution would be finding a multifunctional catalyst system that could detect and degrade/inactivate the poisonous pollutants released in the environment. In this regard, core@shell structured Au nanodendrites@Au nanoclusters (AuND@AuNC) were prepared by a facile one-step inverted process using methionine for pollutant degradation and heavy metal detection. There is no surfactant, polymer, or seed was employed in the preparation of AuND@AuNC. In the preparation of AuND@AuNC, the concentration of AuCl4- was optimized and it was observed that beyond 1.5 mM of Au concentration, formed gold sols aggregate immediately. Prepared AuND@AuNC were characterized well using high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction technique (SAED), X-ray diffraction (XRD), UV-Vis absorption spectroscopy, and X-ray photoelectron spectroscopy (XPS). Interestingly, the prepared AuND@AuNC demonstrates excellent catalytic reduction/degradation of nitroaromatic compounds and organic dye molecules with the aid of sodium borohydride. The results of the kinetic studies confirm the superior catalytic activity of present AuND@AuNC over already published results. Further, AuND@AuNC prepared with 1.5 mM Au concentration exhibits excellent colorimetric sensing behaviour towards cadmium ion (Cd2+) in the presence of 500 µM of interfering ions with a limit of detection of 2.5 µM. The excellent catalytic and sensing behavior of AuND@AuNC material is attributed to its unique structural features and methionine functionalization.

Emissions Merit Function for Evaluating Multifunctional Catalyst Beds

With emission control regulations getting stricter, multi-functional catalyst systems are increasingly important for low-temperature operation. We investigate a wide range of multi-component catalyst systems, as physical mixtures and in multi-bed configurations, while varying the ratios of hydrocarbon traps (HCT), passive NOx adsorbers (PNAs), and diesel oxidation catalysts (DOC). Using industrially guided protocols, we measured the ability of these complex catalyst systems to reduce emissions during a 40 °C/min temperature ramp to simulate cold-start conditions. Using a temperature boundary condition of 250 °C, the average conversion was calculated for each regulated pollutant: CO, NOx, and total hydrocarbons (THC). An emissions merit function was developed to evaluate the effectiveness of each system relative to the relevant emission standards and expected engine exhaust concentrations. This merit function identified that a 1:1:4 ratio of PNA:HCT:DOC was the most effective emissions reduction configuration and had similar reactivity as a physical mixture or as a PNA→HCT→DOC multi-bed reactor.

Thermal behavior and flame retardancy of poplar wood impregnated with furfuryl alcohol catalyzed by boron/phosphorus compound system

The objective of this work was to improve the thermal stability and flame resistance of furfurylated wood via preparing a new multifunctional catalyst system containing boric acid (BA) and ammonium dihydrogen phosphate (ADP). Here, poplar wood (Populus cathayana) was impregnated with furfuryl alcohol (FA)/BA/ADP solutions, followed by curing at 105 ℃ to form a hydrophobic FA resin network within wood. When the BA/ADP system catalyzed in situ polymerization of FA inside the cell wall, the thermal stability was greatly enhanced with the decreasing of the prominent peak of mass-loss rate, the decomposition temperature, and the volatile gases. The limiting oxygen index (LOI) value of the treated wood was as high as 34.4% and its flame retardancy was remarkably improved by suppressing the heat transfer and smoke generation and promoting the char formation during combustion. The flame retardancy index (FRI) value of BA/ADP-FA modified wood was improved by 217%, indicating a “good” flame retardant efficiency. The crosslinking structures like P-O-C and B-O-C bonds enhanced the thermal stability of char. Such resulted poplar wood with flame retardancy will be an excellent application prospect as engineering biomaterial.

Synergistic catalysis within core-shell Fe3O4@SiO2 functionalized with triethylene glycol (TEG)-imidazolium ionic liquid and tetramethylpiperidine N-oxyl (TEMPO) boosting selective aerobic oxidation of alcohols

HypothesisIt is expected that incorporation of 2, 2, 6, 6-tetra-methyl piperidine-N-oxyl radical (TEMPO) and an imidazolium bromide bearing hydrophilic triethylene glycol (TEG) groups on Fe3O4@SiO2 core–shell may not only result in a novel highly water-dispersible/magnetically separable multi-functional catalyst system for metal-free aerobic oxidation of alcohols, which operates through a synergistic relay pathway, but it could potentially provide a strong platform for simultaneous separation and recycling of all components. ExperimentsThe catalyst was prepared by anchoring TEMPO moieties onto a magnetic core–shell Fe3O4@SiO2 functionalized with an ionic liquid bearing TEG groups. The materials was characterized using transmission electron microscopy, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption isotherms, thermal gravimetric analysis, and elemental analysis. The performance of the catalyst was evaluated and quantitatively measured in the aerobic oxidation of alcohols in water. FindingsThe catalyst exhibited excellent and stable colloidal dispersion in water and high performance in the aerobic oxidation of various types of alcohols under metal- and halogen-free reaction conditions. As hypothesized, strong synergistic effect between functionalized components was seen in the described reaction. The catalyst displayed excellent dual-adjustable-selectivity in the oxidation of primary alcohols to either the corresponding aldehydes or carboxylic acids by tuning the reaction solvent and/or reaction time and excellent recycling behavior through a “double-separation-strategy”.

Bifunctional rice husk-derived SiO2-Cu-Al-Mg nanohybrid catalyst for one-pot conversion of biomass-derived furfural to furfuryl acetate

Developing one-pot reaction methodologies, which typically require multifunctional catalyst systems, is crucial for sustainable production of bio-derived fuels and chemicals. This work reports one-pot hydrogenation-esterification of furfural to furfuryl acetate using a bifunctional metal-based nanohybrid catalyst, composed of rice husk (RH) derived SiO2, Cu, Al, and Mg species (RHSiO2-Cu-Al-Mg). For comparison, the catalytic efficiency of RHSiO2-Cu and RHSiO2-Cu-Al were tested under similar reaction conditions. Various analytical techniques were used to elucidate the physicochemical, textural, and acid-redox properties of the catalysts. It was found that the RHSiO2-Cu-Al-Mg catalyst contains an optimum amount of acid and redox sites, as illustrated by NH3-TPD and H2-TPR studies, respectively. Especially, Mg addition played a vital role in tailoring acidity of the RHSiO2-Cu-Al catalyst to promote in-situ esterification of furfuryl alcohol with acetic acid to yield furfuryl acetate. As a result, the RHSiO2-Cu-Al-Mg catalyst exhibited the best performance in one-pot conversion of furfural to furfuryl acetate, outperforming various noble metal/silica based catalysts. This study offers potential opportunities for the rational design of novel, bifunctional heterogeneous catalysts for efficient production of bio-derived fuels and value added chemicals.

Experimental Investigation on the Two-Sided Effect of Acidic HZSM-5 on the Catalytic Performance of Composite Fe-Based Fischer–Tropsch Catalysts and HZSM-5 Zeolite in the Production of Aromatics from CO2/H2

A negative effect of an HZSM-5 zeolite was observed for CO2 hydrogenation toward the production of aromatics when combined with Fe-based Fischer–Tropsch synthesis (FTS) catalysts in an improper manner. The conversions of CO2 and CO were seriously hindered due to suppression in the formation of Fe carbides. With various especially designed experiments, it is confirmed that the Brønsted acid sites in the zeolite serving as an electron acceptor should be the major factor influencing the electron transfer from the Fe phase to CO molecules, resulting in the suppression of CO dissociation. Additionally, we suggested a practical way to eliminate the negative effect of the acidic HZSM-5 zeolite by coating an inert layer on either the Fe-based catalyst or the zeolite. With these observations, it is beneficial to design a multifunctional catalyst system that can be scaled up by paying more attention toward the two-sided effect of zeolites.

Finetuning hierarchical energy material microstructure via high temperature material synthesis route

Hierarchical energy materials such as graphite are a backbone of various scientifically and commercially important emerging technologies including high-energy density energy storage systems with fast charging capability, multifunctional catalyst systems, selective membrane separation systems, and next-generation nuclear material systems. Consequently, it is extremely crucial to develop an efficient and cost-effective route of bulk hierarchical material synthesis (e.g., carbonaceous materials with a well-controlled fraction of the graphitic content) to cater the extraordinary operational and energy material requirements in a very complex coupled thermophysicochemical environment. Here we present a fabrication of Polyacrylonitrile (PAN) derived carbon films and fibers (~with linear dimension ~100 nm) via electrospinning and spin coating methods ensued by a heat-treatment in the range of 1000–3000 °C under inert atmospheric conditions. Intriguingly, we observed at least a two orders of magnitude enhancement (~134%) in length of graphitic plane accompanied by 36% more graphitization when the carbonization temperature increased from 1000 °C to 3000 °C. Such significant enhancements were attributed to the differences in the fundamental nanomorphology of initial carbonaceous materials and their subsequent kinetic evolution as it was more favorable for underlying graphene layers in films to stack and bond to the adjacent ones without strong rotations as compared to fibers, which were further evident from fewer voids and cracks in the films. The covalent cross-links, substrate effect and physical entanglements of carbon domains in PAN-derived carbon films contributed to a higher graphitic length owing to more shear stress between the graphene layers, compared to fibers and undergoes an enormous transformation from turbostratic structures to ordered state along with nitrogen removing over high temperature heating. This morphology dependent graphitization was also investigated from computational approach and concluded in the similar thoughts. The outcomes from this systematic study can be beneficial to the carbon research community focusing in the morphology dependent applications, for instance catalysis, energy storage, sensors etc.

Hydrogen bond activation strategy for cyclic carbonates synthesis from epoxides and CO2: current state-of-the art of catalyst development and reaction analysis

ABSTRACTChemical fixation of CO2 into useful organic compounds has been attracting much attention from the viewpoint of CO2 emission reduction and energy structure reformation. A useful and widely investigated chemical utilization of CO2 is the cycloaddition of CO2 to epoxides for the synthesis of cyclic carbonates. Efforts have been paid to the design and preparation of various catalyst systems that are active and selective to the production of the desired products under mild conditions and in green processes. This article is to review the current state of the catalyst development and the experimental and theoretical analysis of reaction mechanism for the cyclic carbonate synthesis from epoxides, one of currently important reactions involving CO2 as a reactant with 100% atom economy. Particular attention is given to the catalysis of multifunctional catalyst systems such as metal- and hydrogen-bond donor (HBD)-based catalysts.

In situ reduction and stabilization of Ag NPs onto magnetic composites for rapid hydrogenation catalysis

A novel core–shell-structured Ag-based magnetic functional polymer nanocatalyst, i.e., Fe3O4@SN/GLA@chitosan-Ag (SN represents animo-functionalized SiO2, GLA signifies glutaraldehyde), was fabricated via a simple and environmentally friendly method. The magnetic separation property of Fe3O4, the protection effects of SiO2, the reduction and stabilization activities of chitosan, and the catalytic property of Ag nanoparticles (NPs) in the multifunctional catalyst system were efficiently combined using glutaraldehyde as bridging agent. The Ag NPs with average diameter about 2–11 nm were generated in situ and stabilized by chitosan, which acted as reducing agent and stabilizer in the absence of other potentially toxic reagents. Furthermore, the reduction, chelation ability of chitosan, and the size of Ag NPs were found to be tunable, thereby enabling the preparation of other noble metal catalysts with tailored properties. Most importantly, the as-prepared catalyst exhibited superior catalytic performance (the reduction reaction was finished within 3 min) and reusability (reusable for at least six times) in the reduction of 4-nitrophenol.

Selective hydrogenation of nitriles to imines over a multifunctional heterogeneous Pt catalyst

Imines and their derivatives are versatile synthetic intermediates for the industrial preparation of both bulk and fine chemicals and for pharmaceuticals, but preparing these compounds efficiently through direct hydrogenation of nitriles are hindered by overhydrogenation to secondary amines. Here we report a highly efficient multifunctional catalyst system for selective hydrogenation coupling of nitriles to secondary imines using a heterogeneous Pt catalyst that was deposited on a nickel‐based metal‐organic framework (MOF) containing DABCO. The catalyst showed excellent synergy in promoting the hydrogenation of a variety of nitriles, giving significantly improved activity and selectivity (up to >99% yield) even under atmospheric pressure of H2. It is suggested that the Lewis base (DABCO) sites on the Ni‐MOF inhibit further hydrogenation of the imines. The influence of H2 pressure, reactant concentration, stirring speed, and reaction temperature was investigated. The kinetics and mechanism of hydrogenation of benzonitrile (BN) by the Pt/Ni‐MOF catalyst has been studied. The reaction showed a first‐order dependence on both BN concentration and H2 pressure. A kinetic model was proposed based on the mechanism of nitriles hydrogenation and compared with experimental observations. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3565–3576, 2014

ChemInform Abstract: Enantioselective Fluorination Reaction of β‐Ketoester‐Catalyzed Chiral Primary Amine‐Based Multifunctional Catalyst Systems.

AbstractCombination of a cinchona alkaloid‐derived primary amine with L‐leucine gives a dual amine system with promising catalytic activity in enantioselective fluorination reactions of indanone‐2‐carboxylates (I).

Enantioselective Fluorination Reaction of β-Ketoester–Catalyzed Chiral Primary Amine–Based Multifunctional Catalyst Systems

The fluorination reaction is an important organic transformation for asymmetric synthesis. In this article, we reported the determination of chiral primary amine–based multicatalyst systems for enantioselective fluorination of β-ketoester. Studies on the enantioselective organocatalytic fluorination promoted by cinchona alkaloid–derived chiral primary amines in the absence of various co catalysts revealed that the combined metal salts and organocatalysts resulted in poor conversion and enantioselectivities, whereas the combinational use of L-leucine and QN-NH2 as dual primary amine catalysts led to the determination of a novel dual organocatalyst with promising catalytic activity. On the basis of these results, we revealed that the steric environment of the chiral enamine intermediate formed by the condensation of β-ketoester with the chiral primary amine is most responsible for the observed enantioselectivity. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]

Review of fast pyrolysis of biomass and product upgrading

This paper provides an updated review on fast pyrolysis of biomass for production of a liquid usually referred to as bio-oil. The technology of fast pyrolysis is described including the major reaction systems. The primary liquid product is characterised by reference to the many properties that impact on its use. These properties have caused increasingly extensive research to be undertaken to address properties that need modification and this area is reviewed in terms of physical, catalytic and chemical upgrading. Of particular note is the increasing diversity of methods and catalysts and particularly the complexity and sophistication of multi-functional catalyst systems. It is also important to see more companies involved in this technology area and increased take-up of evolving upgrading processes.

The multi-step reactions for the synthesis of C 8 aldehydes and alcohol from propene in a single pot using an eco-friendly multi-functional catalyst system: Kinetic performance for parametric optimization

Kinetics of multi-step reactions including hydroformylation, aldol condensation and hydrogenation was carried out in a single pot for optimization of the reaction parameters for the synthesis of C 8 aldehydes and alcohol from propene using an eco-friendly multi-functional heterogeneous catalyst system [HF/HT] where [HF] = rhodium complex, HRh(CO)(PPh 3) 3 and [HT] = hydrotalcite, Mg 1− x Al x (OH 2) x+ (CO 3 2−) x/ n · mH 2O. The catalyst [HF/HT] was synthesized by impregnation of [HF] onto the surface of [HT]. In the typical catalytic experiments conducted in a 100 mL high pressure reactor under the employed reaction conditions: propene = 10 atm, CO = 5 atm, H 2 = 15 atm, [HF/HT] = 700 mg, HT/HF ratio = 7, Mg/Al molar ratio of [HT] = 3.5, aldol temperature = 250 °C, reaction time = 12 h, agitation speed = 1000 rpm, and in 50 mL toluene as a solvent, 68.4 × 10 −3 M of 2-ethylhexanol with 18% selectivity was achieved. The rates of reactions were determined by analyzing the amounts of products formed at different time using gas chromatography. Kinetics of the various reactions were performed in detail by investigating the effect of reaction parameters such as Mg/Al molar ratio of [HT] at aldol temperature 150 and 250 °C, amount of [HT] and [HF] complex, aldol temperature, partial pressure of CO and H 2 on the rates of formation of products namely, 2-ethylhexanol, 2-ethylhexanal, 2-ethylhexenal, butanals and butanols. The rates of reactions were found to be influenced by all these studied parameters. On increasing these parameters, the rates of formation of the products and their further conversions in single pot were favored.

Some features and the mechanism of regulation of the molecular-mass distribution of products of ethylene oligomerization in the presence of zirconium-containing metal complex systems (A review)

It was shown that the deviation of the product distribution from the Schultz-Flory law upon ethylene oligomerization in the presence of some catalytic systems based on zirconium compounds is due to their multisite character and a multiroute mechanism of the process. The feasibility of switching the base multiroute multisite multifunctional catalyst systems to monofunctional operation with a narrow molecular-mass distribution (MMD) of oligomerization products was shown using zirconyl carboxylate systems as an example. A comparative evaluation of the kinetic parameters of individual ethylene oligomerization steps and an analysis of the behavior of the MMD in the presence of three different catalyst systems were performed. A possible mechanism of regulation of the character and width of the MMD of the oligomerization products is discussed.

R&D activities of fuel cell Research at KFUPM

Development of systems with reduced emission of pollutants is one of the major challenges of this century. Fuel cells promise to provide clean and renewable source of energy, which can operate on many fuels. They are promising candidates for transportation and portable power source applications. These applications include battery replacement for potable telephones and computers, power sources in remote areas, etc. Fuel cells can also work using other fuels such as hydrocarbons including methanol either directly or indirectly. Since there is plenty of hydrocarbons resources available in the Gulf region such as gasoline, naphtha, and methane/natural gas etc., they can be utilized in the fuel cell to produce clean power without combustion. There has been tremendous research effort in other parts of the world, especially the Western world for the development of fuel cells. Research at KFUPM is focused on two different aspects, fuel for fuel cells (reformat feed) and PEM fuel cell system. Our research group at KFUPM is actively involved in fuel cell research since 1980s. Current focus is to develop PEM fuel cell system emphasizing three different aspects: (A) developing novel low cost proton conducting membranes, (B) developing multifunctional catalyst system and (C) development of hydrocarbon based fuel processing systems. In this communication research activities and/ongoing projects undertaken at KFUPM for fuel cell development will be presented.

The ‘single-pot’ synthesis of C 2 n+2 -aldol derivatives from C n-alkenes using multi-functional catalyst

A multi-functional catalyst [HF/HT], by impregnation/intercalation of inorganic metal complex, HRh(CO)(PPh 3) 3 [HF] on a solid base hydrotalcite; ( Mg 1 - x Al x ( OH 2 ) ) x + ( ( CO 3 2 - ) x / n · m H 2 O ) [HT] having hydroformylation, aldol condensation and hydrogenation activity is reported for synthesis of C 2 n+2 -aldol derivatives from C n -alkenes in single pot. The effect of the, HT/HF weight ratio, Mg/Al molar ratio of HT and aldol condensation temperature ( T 2) at a fixed hydroformylation temperature ( T 1) is studied for single pot synthesis of C 8 aldol derivatives from propylene using [HF/HT] catalyst system under varied reaction parameters. The selectivity of 2-ethylhexanal is observed to increase from 7% to 48% by increasing the HT (Mg/Al = 3.5) to HF ratio from 1 to 10. The selectivity of 2-ethylhexanol increased from 11% to 21% on increasing the Mg/Al molar ratio of HT from 1.5 to 3.5 in the multi-functional catalyst system at aldol condensation temperature ( T 2) 250 °C.

Single-step synthesis of dimethyl ether in a slurry reactor

Dimethyl ether (DME) is an important intermediate in several alternative fuels processes which ultimately convert synthesis gas to liquid products. Our work details a novel slurry-based process which yields DME and variable amounts of co-product methanol (MeOH) from synthesis gas in a single step. The water-gas shift, MeOH synthesis, and MeOH dehydration reactions proceed concurrently in a three-phase reactor. Operation with a back-mixed slurry reactor exploits the synergy of the three reactions, and moderates the reaction exotherm to permit high per-pass conversions. Feed gases with CO concentrations ranging from 20% to 60%, and H 2/CO ratios varying from 0.01 to 2.9 have been tested with several multi-functional catalyst systems. The process offers the potential for both lower capital and operating costs compared to processes using independent shift, MeOH, and DME reactors.

Hybrid simulation of multicomponent chemical reactions in multifunctional catalyst systems

At the Laboratory of Chemical Technology of the Delft University of Technology, research work is carried out on problems in which multicomponent chemical reactions in a bifunctional catalyst environment are a principal element. Study of the interrelated effects of the many system parameters, as well as the search for possible opti maZ catalyst compositions to maximize output and yield, has made it desirable to have at hand a fast simulation of the reaction system. Hybrid computation appeared to be the logical way to meet the needs of the above Laboratory for easy man- machine interaction and high computation speed. In this report are presented the development and imple mentation of the hybrid simulation together with some of its results as realized at the Delft University Computation Centre. The hybrid model at present simulates a five-component reaction using a bifunc tional catalyst. Much effort has been invested to obtain both easy input/output and the highest possible speed of solution using an Applied Dynamics AD4, an IBM 1800, and interface equipment. How this was done is described in some detail.

Mass transport and chemical reaction in multifunctional catalyst systems

A number of reactions of industrial significance take place in two or more kinetically distinct steps, each of which may be effectively promoted by different types of catalyst. The promotion of some classes of consecutive and concurrent reactions by a dual functional catalyst is considered. It is shown that both rate of reaction and yield are affected by the catalyst formulation, and that when the reaction duty is defined there exists an optimum catalyst formulation.