Composite Catalyst System Research Articles

Super-fast hydrogen generation via super porous Q-P(VI)-M cryogel catalyst systems from hydrolysis of NaBH4

Novel poly(1-vinyl imidazole) p(VI) cryogels were synthesized via cryopolymerization technique where simultaneous polymerization and crosslinking occur around ice crystals under freezing conditions. The superporous p(VI) cryogels were modified with various alkyl bromides possessing different chain lengths such as 1.2-Dibromoethane (1,2-BE), 1.4-Dibromobutane (1,2-BB) and 1.6-Dibromohexane (1,6-BH), and used as template for in situ metal nanoparticle (M) synthesis (M: Co0 or Ni0). The prepared p(VI)-M cryogel composites were used in hydrogen (H2) generation from the hydrolysis of sodium borohydride (NaBH4). Very high turnover frequency (TOF) and H2 generation rate (HGR) values, of 34.4 (mol H2) (mol catalyst min)−1 and 14566.9 (mL H2) (min)−1 (g of M)−1, respectively, were obtained at 70 °C for 3rd time Co (II) loaded and reduced 1.2-BE modified p(VI)-Co composite catalyst system compared with other imidazole-based catalyst systems reported in the literature. Moreover, modified p(VI) cryogels possess inherently magnetic behavior even after a single Co(II) loading-reduction step. Due to their superior properties, such as being recoverable via external applied magnetic field, fast HGR, and reusability, 1.2-BE-p(VI)-Co metal composites were found to be a highly attractive catalyst system for catalytic hydrolysis of NaBH4.

The Use of Metal Nanoparticle-Embedded Poly(ethyleneimine) Composite Microgel in the Reduction of Nitrophenols

Metal nanoparticles such as Ni, Cu, and Co were prepared within polyethyleneimine (PEI) microgels and were used in the reduction of 4-nitrophenol (4-NP) and 2-nitrophenol (2-NP) to 4-aminophenol (4-AP) and 2-aminophenol (2-AP). The metal nanoparticle content of the prepared PEI-M composite catalyst system (M = Co, Ni, and Cu) was increased by multiple loading and reduction cycles into PEI microgels to provide faster and better reduction of 4-NP and 2-NP. The TOF value increased to 1.48 from 0.353 (mol 4-NP (mol catalyst min)−1) for 4-NP reduction catalyzed by PEI-Ni after three cycles of metal loading and reduction. The effect of temperature on 4-NP and 2-NP reductions catalyzed by PEI-M illustrated that higher temperature resulted in very fast reductions, e.g., at 70 °C 4-NP and 2-NP reduction by PEI-Ni resulted in very fast reduction times of 1.2 and 0.67 min to 4-AP and 2-AP, respectively. The activation parameters, such as energy, entropy, and enthalpy, were also calculated and mild activation energies of 38.8 and 46.0 kJ mol−1 for 4-NP and 2-NP catalyzed by PEI-Ni were found, respectively, in comparison to similar studies in the literature. Moreover, it was demonstrated that PEI-Ni microgels are reusable five times consecutively, with almost 100 % conversion and 100 % of their catalytic activity.

Superporous P(2-hydroxyethyl methacrylate) cryogel-M (M:Co, Ni, Cu) composites as highly effective catalysts in H2 generation from hydrolysis of NaBH4 and NH3BH3

Highly porous p(2-hydroxyethyl methacrylate) p(HEMA) cryogels were synthesized via cryopolymerization technique and used as template for Co, Ni, and Cu nanoparticle preparation, then as composite catalyst systems in H2 generation from hydrolysis of both NaBH4 and NH3BH3. Due to their highly porous and open microstructures, p(HEMA)-Co cryogel composites showed very effective performances in H2 production from hydrolysis of both chemical hydrides. The characterization of p(HEMA) cryogels, and their metal composites was determined via various techniques including swelling experiments, digital camera images, SEM and TEM images, AAS and TGA measurements. The effect of various parameters on the hydrolysis reaction of NaBH4 such as metal types, concentration of chemical hydrides, amounts of catalyst, alkalinity of reaction medium and temperature were investigated in detail. It was found that Co nanoparticles are highly active catalysts in H2 generation reactions from both hydrides. The hydrogen generation rate (HGR) of p(HEMA)-Co was 1596 (mL H2) (min)−1 (g of Co)−1 which is quite good in comparison to reported values in the literature. Furthermore, kinetic parameters of p(HEMA)-Co metal composites such as energy, enthalpy and entropy were determined as Ea = 37.01 kJmol−1, ΔH# = 34.26 kJmol−1, ΔS# = −176,43 Jmol−1 K−1, respectively.

Metal nanoparticle-embedded super porous poly(3-sulfopropyl methacrylate) cryogel for H2 production from chemical hydride hydrolysis

Poly(3-sulfopropyl methacrylate) (p(SPM)) cryogel was prepared under cryogenic conditions (T = −18 °C) and used as template for in situ metal nanoparticle preparation of Co, Ni and Cu. These metal nanoparticle-containing super macroporous cryogel composites were tested for H2 production from hydrolysis of sodium borohydride (NaBH4) and ammonia borane (AB). It was found that amongst p(SPM)-M (M: Co, Ni, and Cu) composite catalyst systems, the catalytic performances of Co- and Ni-containing p(SPM) cryogel composite catalyst systems were the same, however in hydrolysis of NH3BH3, the order of performance of the catalysts was Co > Ni > Cu. Interestingly, p(SPM)-Co cryogel composite demonstrated better catalytic performances in salt environments e.g., faster H2 production rate in sea and tap water compared to DI water, and almost no effect of ionic strength of the solution medium was observed, but the salt types were found to affect the H2 generation rate. Other parameters that affect H2 production rate such as metal type, temperature, water source, salt concentration, amount of metal nanocatalyst and reusability were investigated. It was found that the hydrogen generation rate (HGR) was increased to 2836 ± 90 from 1000 ± 53 (ml H2)(g of Co min)−1 by multiple loading and reduction cycles of Co catalyst. Also, it was found that TOF values are highly temperature dependent, and increased to 15.1 ± 0.8 from 2.4 ± 0.1 (mol H2)(mol catalyst min)−1 by increasing the temperature from 30 to 70 °C. The activation energy, activation enthalpy and activation entropy were determined as 40.8 kJ (mol)−1, 37.23 kJ (mol K)−1, and −170.87 J (mol K)−1, respectively, for the hydrolysis reaction of NaBH4 with p(SPM)-Co catalyst system, and 25.03 kJ (mol)−1, 22.41 kJ (mol K)−1, and −182.8 J (mol K)−1, respectively, for AB hydrolysis catalyzed by p(SPM)-Co composite system.

Superior reusability of metal catalysts prepared within poly(ethylene imine) microgels for H2 production from NaBH4 hydrolysis

Polyethylene imine (PEI) particles were synthesized by a microemulsion polymerization technique, and were used as template for metal nanoparticle preparation. The PEI particles were loaded with Co(II), Ni(II) and Cu(II) ions from water and with CoCl2, NiCl2 and CuCl2 from ethanol and treated with NaBH4 to reduce the corresponding metal nanoparticles in situ. The PEI-M (Co, Ni, and Cu) composites were used in hydrogen generation from the hydrolysis of NaBH4 and NH3BH3 (AB). The PEI-Co composite catalyst system had better catalytic performances in the hydrolysis reactions of NaBH4 and AB than the other metal containing composites. The turnover frequency (TOF) value of PEI-Co in the hydrolysis of AB was found to be almost 12.5 fold more than NaBH4 hydrolysis. It is reported here that the PEI template offered better characteristics than the other templates providing many advantages; for example, the metal loading capacity of PEI increased by sequential loading and reduction cycles, and very high conversion (100%) and activity (100%) were obtained when PEI-Ni was used in fifteen consecutive runs for NaBH4 hydrolysis. The PEI-M composites have mild activation energy in comparison to the literature but better, more flexible characteristics, and very fast kinetics in AB hydrolysis.

Metal ion-imprinted hydrogel with magnetic properties and enhanced catalytic performances in hydrolysis of NaBH4 and NH3BH3

Metal ion-imprinted (IIH) poly(2-acrylamido-2-methyl-1-propansulfonic acid) p(AMPS) hydrogels were prepared by using a free-radical polymerization technique in the presence of metal ions (M = Co (II) or Ni (II)). Using metal ion-imprinted hydrogels (IIHs), and non-metal ion-imprinted (NIH) hydrogels as template for the preparation of Co and Ni catalyst systems, the hydrolysis kinetics of NaBH4 and NH3BH3 were investigated. The catalytic performances of IIHs and NIHs were compared in terms of effect on hydrolysis kinetics of NaBH4 and NH3BH3. To increase the amounts of Co nanoparticles within p(AMPS) hydrogel for better catalytic activity, several reloading and reduction cycles of Co (II) ions were carried out, and the prepared p(AMPS)-Co composite catalyst systems were tested for hydrogen generation from the hydrolysis of NaBH4. As the number of Co (II) loading and reduction cycles increased, the amount of metal catalysts and the catalytic performance of composites increased. Kinetics studies were carried out on three times Co (II) ion loaded and reduced p(AMPS)-Co catalyst systems (containing 36.80 mg/g Co). Three time Co (II)-loaded catalyst systems provided very fast hydrolysis kinetics for NaBH4, and provided magnetic field responsive behavior. The hydrolysis reaction of NaBH4 was completed within 50 s, under the described conditions at 60 °C. It was demonstrated that the synthesized catalyst systems can be used ten times repetitively without significant loss of catalytic activity (86.5%).

Solvent-Free Friedel-Crafts Acylation of Fluorobenzene Catalyzed by Trifluoromethanesulfonic Acid and Rare Earth Triflates

Solvent-free Friedel-Crafts acylation of fluorobenzene with benzoyl chloride was investigated over the trifluoro- methanesulfonic acid (TfOH) and rare earth triflate (Re(OTf)3) composite catalyst. The results showed that the presence of Re(OTf)3 leads to the decrease in a half amount of TfOH catalyst, and there is a synergistic effect between TfOH and Re(OTf)3 in this composite catalyst. For the solvent-free acylation of fluorobenzene with benzoyl chloride, the catalytic activities of 11 kinds of rare earth elements Re(OTf)3 were tested, and it was found that among all Re(OTf)3 compounds La(OTf)3 exhibits the best catalytic performance and it can be repeatedly used. After the acylation of fluorobenzene with benzoyl chloride over the La(OTf)3 and TfOH catalyst at 140 ℃ for 4 h, the selectivity and yield to para-product fluorobenzophenone reach up to 99% and 87%, respectively. For the acylation of different benzene derivatives with benzoyl chloride over the TfOH and Re(OTf)3 catalyst, the promoting catalysis of different elements Re(OTf)3 is different, for instance, for the acylation of dimethylbenzene, Ce(OTf)3 exhibits the best catalytic performance among the tested Re(OTf)3 promoters. Keywords Trifluoromethanesulfonic acid and rare earth triflate; Fuorobenzene; Benzoyl chloride; Friedel-Crafts acylation; Composite catalyst system.

P(AAGA) hydrogel reactor for in situ Co and Ni nanoparticle preparation and use in hydrogen generation from the hydrolysis of sodium borohydride

A hydrogel prepared from 2-acrylamidoglycolic acid monohydrate (AAGA), denoted by p(AAGA), was used for Co and Ni nanoparticle preparation within the hydrogel matrix. The p(AAGA)–M (M: Co, Ni) composite system was also shown to be capable of carrying out an aqueous reaction effectively, i.e., the hydrolysis of NaBH4 for hydrogen generation. The reaction kinetics are investigated under different reaction conditions and various parameters, such as initial NaBH4 concentration, temperature, catalyst amounts and types, affecting the hydrolysis process of NaBH4 were evaluated. The activation energies for the hydrolysis of NaBH4 were calculated to be 43.77kJmol−1 and 26.62kJmol−1for p(AAGA)–Ni and p(AAGA)–Co catalyst systems, respectively. Even after seven repetitive uses p(AAGA)–Co composite catalyst system had 100% conversion with 95% activity. More importantly, the p(AAGA)–Co system has proven to have very good storage capacity, e.g., after 30-day storage time, p(AAGA)–Co had no loss in conversion and had 68% catalytic activity.

A novel p(AAm-co-VPA) hydrogel for the Co and Ni nanoparticle preparation and their use in hydrogel generation from NaBH4

A novel bulk poly(acrylamide-co-vinyl phosphonic acid) (p(AAm-co-VPA)) hydrogels were synthesized via a photo polymerization technique in macro dimension. Ni and Co nanoparticles inside p(AAm-co-VPA) hydrogel were also prepared by reduction of the metal ions loaded into the hydrogel network from the corresponding metal salt solution in water. The reduction of these bound metal ions within hydrogel matrices were done by treating hydrogel-laden metal ions with NaBH4 to produce novel hydrogel-metal composite catalyst systems. Furthermore, these soft hydrogel composite catalyst systems were employed in the generation of hydrogen from the hydrolysis of sodium boron hydride (NaBH4) in a basic medium. Thermogravimetric analysis (TGA) and atomic absorption spectroscopy (AAS) measurements were employed to determine the metal particle content of p(AAm-co-VPA)-M (M: Co, Ni) composite hydrogels. The effects of different parameters such as the amount of catalyst, the reaction temperature, the type of the metal, the initial concentration of NaBH4 and reusability of the prepared catalyst systems were investigated, and the activation energy for hydrolysis of NaBH4 by p(AAm-co-VPA) was found as 23.68kЈ/mol.

Superabsorbent hydrogels for cobalt nanoparticle synthesis and hydrogen production from hydrolysis of sodium boron hydride

Polymeric hydrogels derived from 2-acrylamido-2-methyl-1-propansulfonic acid (AMPS) were utilized in the preparation of cobalt (Co) metal nanoparticles and used as a composite–catalyst system in hydrogen generation from the hydrolysis of NaBH4. The embedded Co nanoparticles in the p(AMPS) networks are on the order of 100nm. It was demonstrated that the p(AMPS)–Co composite system was very effective in the production of hydrogen from alkali aqueous sodium boron hydride solutions. The effect of various parameters such as the initial concentration of NaBH4, the amount of catalyst and temperature on the hydrolysis reaction was evaluated. The activation energy for hydrogen production by Co particles was found to be 38.14kJmol−1; while the activation enthalpy was 35.46kJmol−1.

Dehydrogenation of Ethylbenzene to Styrene with Carbon Dioxide Over ZrO2-based Composite Oxide Catalysts

We have been exploring various new catalyst systems for the utilization of carbon dioxide as a soft oxidant in the catalytic dehydrogenation of ethylbenzene (EB) to styrene. The utilization of CO2 as a soft oxidant for the commercially important catalytic dehydrogenation of EB to styrene has received enormous attention recently due to its several attractive features. This review summarizes the results of our most recent findings on zirconia-based composite oxide catalyst systems exploited for this reaction. Under this systematic and comprehensive investigation various zirconia-based composite oxide catalysts namely, TiO2-ZrO2, MnO2-ZrO2, CeO2-ZrO2, K2O/TiO2-ZrO2, B2O3/TiO2-ZrO2 and CeO2-ZrO2/SBA-15 have been synthesized, characterized by various techniques and evaluated for the title reaction. Most of these composite oxide catalysts were found to exhibit very interesting physicochemical characteristics and exceptionally better catalytic properties for this reaction. As revealed by characterization results, a large number of acid–base sites with moderate strength are essential for a high conversion and product selectivity of this reaction with CO2 as the soft oxidant.

Condensation reaction of formaldehyde and methyl formate catalyzed by a composite catalyst system

The condensation reaction of formaldehyde and methyl formate to form methyl glycolate and methyl methoxy acetate catalyzed by p-toluenesulfonic acid and different Lewis acid compounds has been investigated. The composite catalytic system consisting of p-toluenesulfonic acid and NiX 2 (X = Cl, Br, I), especially NiI 2, exhibited a high catalytic performance for the condensation reaction, the total yield of MG and MMAc was up to 72.37%.

A mechanism study on preparation of rayon based carbon fibers with (NH 4) 2SO 4/NH 4Cl/organosilicon composite catalyst system

The mechanisms of the preparation of rayon based carbon fibers with (NH 4) 2SO 4/NH 4Cl/organosilicon composite catalyst system were studied. The thermal behaviors of rayon fibers that were treated with different catalysts were studied by thermogravimetry–mass spectrometry (TG–MS) and the surface of treated rayon fibers was studied by scanning electron microscopy (SEM) analysis. Our data showed that the composite catalyst treated rayon fibers underwent pyrolysis under lower temperatures and in a wider range of temperatures. Rayon based carbon fibers prepared with different catalyst system showed different mechanical properties. The presence of (NH 4) 2SO 4/NH 4Cl/organosilicon increased the production of H 2O, CO 2, CO and decreased the production of tar, aldehyde, furan and phenol derivatives. The composite catalyst also promoted the pyrolysis reaction of rayon fibers by lowering its activation energy. Organosilicon seemed to have two aspects of effects on the process of preparing rayon based carbon fibers. It could enhance the penetrability of (NH 4) 2SO 4/NH 4Cl to the interior of rayon fibers and protect the fiber surface in the pyrolysis process. Moreover, organosilicon may participate in the crosslinking reactions of rayon fibers and enhance the drawability of rayon fibers in carbonization process. Our experiments demonstrated that (NH 4) 2SO 4/NH 4Cl/organosilicon was an effective composite catalyst system in the preparation of rayon based carbon fibers.

D078 an X-ray Diffraction Investigation of Nanomaterial Used in Composite Catalyst Systems—Invited

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Selective Catalytic Reduction of Nitric Oxide by Ammonia over Egg-Shell MnOx/NaY Composite Catalysts

A novel composite catalyst system for the selective catalytic reduction (SCR) of NOx by NH3 is described operating at temperatures lower than 470 K in the presence of water with NO conversions of 80–100% at space velocities of 30,000–50,000 h−1. The catalyst is prepared by egg-shell precipitation of MnO2 on the external surface of zeolite NaY. Structural and thermal stability of precipitated MnO2 as well as of the MnO2/NaY composite catalyst were characterized by N2 adsorption, X-ray diffraction, laser Raman spectroscopy, temperature-programmed reduction, and electron microscopy. MnO2 precipitated on zeolite NaY (15 wt% loading) retained its amorphous state up to calcination temperatures of 775 K. The zeolite component remained structurally intact. Calcination at higher temperatures destroyed the zeolite structure and transformed MnO2 into Mn3O4. DRIFT spectroscopic investigations revealed the presence of symmetric ON—O—NO species formally corresponding to N2O3 on the composite catalyst after contact with NO. Catalytic measurements under integral flow conditions showed that the catalyst performance is associated with a close coupling of nitrite formation and its drain off from equilibria with NO/NO2 and nitrate by ammonia. Several results are in line with the “diazotation” mechanism, including NH3 protonation to NH4+, whereas prevailing Lewis acid sites should enable NH3 activation via amide species, thus leading to a parallel “amide/nitrosamide” SCR reaction route. The activity-temperature profile fulfills the requirements of a low-temperature NOx reduction catalyst for mobile diesel engines if an ammonia supply is implemented “on board,” e.g., by urea decomposition.

Hydrodechlorination of chlorinated hydrocarbons over metal–carbon composite catalysts prepared by a modified carbothermal reduction method

A highly stable and active Pd–Fe carbon composite catalyst system for hydrodechlorination of chlrohydrocarbons is obtained by a novel modified carbothermal reduction method using ion exchange resins.

Hydrogenation of carbon dioxide over copper-pyrochlore/zeolite composite catalysts

The hydrogenation of CO 2 was studied over composite catalysts obtained by mixing Cu-based methanol synthesis catalyst and HY zeolite. A mechanism associating methanol synthesis and MTG (methanol to gasoline) reaction allowed the formation of C 1-C 4 hydrocarbons. It was found that the catalytic behaviors of the composite catalysts were favorably influenced by the characteristics of the methanol synthesis catalysts. The Cu-La 2Zr 2O 7 catalyst we recently developed associated with HY zeolite exhibited interesting performances in hydrocarbon synthesis. The addition of ZrO 2 to CuLa 2Zr 2O 7/HY enhanced the ability to produce hydrocarbons. Comparing composite catalyst systems prepared with different Cu-based methanol synthesis catalysts, the effect of Na contamination on methanol and hydrocarbon formation over composite catalysts were also discussed.

Development of composite catalysts made of Cu-Zn-Cr oxide/zeolite for the hydrogenation of carbon dioxide

The hydrogenation of carbon dioxide using a Cu-Zn-Cr oxide/zeolite composite catalyst system has been studied. The change in the structure of the oxide catalyst during the reaction was found to be very significant, with the catalytic activity decreasing rapidly at temperatures over 350°C. Measurement of metallic copper surface areas revealed a sharp decrease in exposed metallic copper caused by the sintering of the catalyst. The reaction of methanol over various composite catalyst was also examined. The results indicated that composite catalysts with low metallic copper surface areas promote the methanol to gasoline reaction, while high surface areas caused the decomposition of methanol to carbon monoxide and carbon dioxide. These results suggested that hydrocarbon synthesis and the decomposition of methanol are competitive.

Development of composite catalysts made of Cu-Zn-Cr oxide/zeolite for the hydrogenation of carbon dioxide

The hydrogenation of carbon dioxide using a Cu-Zn-Cr oxide/zeolite composite catalyst system has been studied. The change in the structure of the oxide catalyst during the reaction was found to be very significant, with the catalytic activity decreasing rapidly at temperatures over 350°C. Measurement of metallic copper surface areas revealed a sharp decrease in exposed metallic copper caused by the sintering of the catalyst. The reaction of methanol over various composite catalyst was also examined. The results indicated that composite catalysts with low metallic copper surface areas promote the methanol to gasoline reaction, while high surface areas caused the decomposition of methanol to carbon monoxide and carbon dioxide. These results suggested that hydrocarbon synthesis and the decomposition of methanol are competitive.