Fabrication of carbon nanofiber by pyrolysis of freeze-dried cellulose nanofiber

The possibility of fabricating carbon nanofibers from cellulose nanofibers was investigated. Cellulose nanofiber of ~50 nm in diameter was produced using ball milling in an eco-friendly manner. The effect of the drying techniques of cellulose nanofibers on the morphology of carbon residue was studied. After pyrolysis of freeze-dried cellulose nanofibers below 600 °C, amorphous carbon fibers of ~20 nm in diameter were obtained. The pyrolysis of oven-dried precursors resulted in the loss of original fibrous structures. The different results arising from the two drying techniques are attributed to the difference in the spatial distance between cellulose nanofiber precursors.     

Glycerol hydrogenolysis to propylene glycol

A nickel catalyst showed a considerable selectivity to propylene glycol (up to 98%) at 30% glycerol conversion, under moderate hydrogenation conditions: 200 °C reaction temperature, 20–25 bar hydrogen pressure, 5 wt% catalyst and unprecedented low reaction time of 8 h.     

Synthesis of highly dispersed Pd/C electro-catalyst with high activity for formic acid oxidation

In this study, we present a simple process to obtain highly dispersed palladium nanoparticles on Vulcan XC-72R carbon support without any protective agent. To obtain high metal loading Pd/C catalyst without any surfactant, we modified the polyol process by employing NH₃ species as a mediation to control the reaction pathway to avoid the precipitation of Pd(OH)₂, and hence the agglomeration of Pd nanoparticles. The obtained Pd/C sample was characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM) techniques. The results show that highly dispersed Pd/C catalyst with an average diameter of 3.0 nm could be obtained in this novel process. The activity of formic acid oxidation on this Pd/C catalyst was examined via cyclic voltammetry technique and it is found that the catalytic activity is greatly enhanced due to the reduced particle size and the improved dispersion of palladium nanoparticles on the carbon surface.     

Structures and cyclization behaviors of gel-spun cellulose/polyacrylonitrile composite fibers

Polyacrylonitrile (PAN)/cellulose composite fibers have been produced by dry-jet gel spinning through their co-solution. The rheological properties of PAN/cellulose/dimethylacetamide/LiCl solutions containing different cellulose contents from 0 to 10 wt% were characterized, and 5 wt% PAN/cellulose composite solution shows the best solution homogeneity. During gel spinning, the cellulose forms elongated particles inside the gelation bath, and the particle diameters depend on the as-spun draw ratio. It was found that the glass transition of PAN fibers shifts to higher temperatures along with the increase of cellulose content, and the glass transition activation energy of PAN chains becomes higher when cellulose particles become smaller. Regardless the changes of cellulose amount (2–10 wt%) and particle diameter (7.1–1.4 μm), the cyclization activation energy of PAN/cellulose composite fibers is 13–17% lower than that of neat PAN fibers. Our experiments suggest that the addition of cellulose in PAN fibers has no direct effect on the cyclization reaction of PAN chains. Instead, the released by-products during the pyrolysis of cellulose at high temperature degradation affect the cyclization reaction of PAN chains.     

Mise en oeuvre d'un catalyseur actif pour l'hydrogenation selective du furanne en tetrahydrofuranne

The selective hydrogenation of furan into tetrahydrofuran was achieved at low temperature and pressure (100 °C, 20 bar) by use of Pd supported on carbon B (5% metal; microporous support). High conversion rates, 150 ml of THF/g of catalyst/h or high turnover frequencies, 2400 h⁻¹, were obtained when the catalyst was washed with distilled water and used in the absence of furfural or carbon monoxide. No significant modification of the catalyst was shown by EDAX analysis. XPS experiments revealed that palladium was initially covered by adsorbed oxygen molecules, and after catalysis Pd° was found. The catalytic activity decreased in the course of the runs: by ESCA analysis the Pd (3d) peak intensity was weaker after 10 runs; thus loss of metal occurred, together with, presumably, the recombination of the metal aggregates.     

Encapsulation of Palladium Carbide Subnanometric Species in Zeolite Boosts Highly Selective Semihydrogenation of Alkynes

The selective hydrogenation of alkynes to alkenes is a crucial step in the synthesis of fine chemicals. However, the widely utilized palladium (Pd)-based catalysts often suffer from poor selectivity. In this work, we demonstrate a carbonization-reduction method to create palladium carbide subnanometric species within pure silicate MFI zeolite. The carbon species can modify the electronic and steric characteristics of Pd species by forming the predominant Pd−C₄ structure and, meanwhile, facilitate the desorption of alkenes by forming the Si−O−C structure with zeolite framework, as validated by the state-of-the-art characterizations and theoretical calculations. The developed catalyst shows superior performance in the selective hydrogenation of alkynes over mild conditions (298 K, 2 bar H₂), with 99 % selectivity to styrene at a complete conversion of phenylacetylene. In contrast, the zeolite-encapsulated carbon-free Pd catalyst and the commercial Lindlar catalyst show only 15 % and 14 % selectivity to styrene, respectively, under identical reaction conditions. The zeolite-confined Pd-carbide subnanoclusters promise their superior properties in semihydrogenation of alkynes.     

Promotion of lanthanum-supported cobalt-based catalysts for the Fischer–Tropsch reaction

This paper focuses on the effect of the La/Co ratio on the structure of alumina cobalt supported catalysts for Fischer–Tropsch synthesis. Catalysts are prepared by wetness impregnation of alumina followed by calcination in air. The catalysts contain 10 wt% of cobalt and between 0 and 20 wt% of La (0, 5, 10, 15, 20). The catalysts were activated by reduction in hydrogen at 673 K and the catalytic performance was evaluated in a fixed bed reactor at 20 bar and 493 K. A wide range of techniques (BET, XRD, TPR, and XPS) were used for catalyst characterization at each preparation step and showed strong impact of the La/Co ratio on the structure, reducibility of supported cobalt phases. It was shown that 10 wt% of lanthanum allows reducing cobalt aluminate and improving catalytic performances.     

Synthesis and characterization of Pd catalysts supported on carbon microspheres for formic acid oxidation

A facile preparation of Pd catalyst using carbon microspheres as support was introduced in this paper. The carbon microspheres were prepared with a simple method from dextrose via hydrothermal process and used as catalysts support for formic acid electrooxidation. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses revealed that the as-prepared face-centered cubic crystal Pd nanoparticles were well-dispersed on the surface of the carbon microspheres, and the mean diameter of the nanoparticles was 8.8 nm. The effect of the support on the catalyst performance for formic acid electrooxidation was studied. The as-prepared catalyst showed the enhanced electrochemical surface active area and the higher electrocatalytic activity towards formic acid oxidation compared with Pd/CNTs and Pd/XC-72 catalysts prepared at room temperature. Electrochemical analysis suggested that the carbon microspheres might be good candidates to be used as the supports of catalyst for formic acid electrochemical oxidation.     

Properties of Pd–Ag/C catalysts in the reaction of selective hydrogenation of acetylene

Samples of Pd/C and Pd–Ag/C, where C represents carbon nanofibers (CNFs), are synthesized by methane decomposition on a Ni–Cu–Fe/Al₂O₃ catalyst. The properties of Pd/CNF are studied in the reaction of selective hydrogenation of acetylene into ethylene. It is found that the activity of the catalyst in hydrogenation reaction increases, while selectivity decreases considerably when the palladium content rises. The obtained dependences are caused by the features of palladium’s interaction with the carbon support. At a low Pd content (up to 0.04 wt %) in the catalyst, the metal is inserted into the interlayer space of graphite and the catalytic activity is zero. It is established by EXAFS that the main share of palladium in catalysts of 0.05–0.1 wt % Pd/CNF constitutes the metal in the atomically dispersed state. The coordination environment of palladium atoms consists of carbon atoms. An increase in the palladium content in a Pd/CNF catalyst up to 0.3 wt % leads to the formation of highly dispersed (0.8–1 nm) Pd particles. The Pd/CNF samples where palladium is mainly in the atomically dispersed state exhibit the highest selectivity in the acetylene hydrogenation reaction. The addition of silver to a 0.1 wt % Pd/CNF catalyst initially probably leads to the formation of Pd–Ag clusters and then to alloyed Pd–Ag particles. An increase in the silver content in the catalyst above 0.3% causes the enlargement of the alloyed particles and the palladium atoms are blocked by a silver layer, which considerably decreases the catalytic activity in the selective hydrogenation of acetylene.     

Development of magnetic,ferrite supported palladium catalysts for 2,4-dinitrotoluene hydrogenation

Cobalt, copper, and nickel ferrite spinel nanoparticles have been synthesized by using a combination of sonochemical treatment and combustion. The magnetic nanoparticles have been used as supports to prepare ~4 wt% palladium catalysts. The ferrites were dispersed in an ethanolic solution of Pd(II) nitrate by ultrasonication. The palladium ions were reduced to metallic Pd nanoparticles, which were then attached to the surface of the different metal oxide supports. Thus, three different catalysts (Pd/CoFe₂O₄, Pd/CuFe₂O₄, Pd/NiFe₂O₄) were made and tested in the hydrogenation of 2,4-dinitrotoluene (DNT). A possible reaction mechanism, including the detected species, has been envisaged based on the results. The highest 2,4-diaminotoluene (TDA) yield (99 n/n%) has been achieved by using the Pd/NiFe₂O₄ catalyst. Furthermore, the TDA yield was also reasonable (84.2 n/n%) when the Pd/CoFe₂O₄ catalyst was used. In this case, complete and easy recovery of the catalyst from the reaction medium is ensured, as the ferrite support is fully magnetic. Thus, the catalyst is very well suited for applicationy in the hydrogenation of DNT or other aromatic nitro compounds.     

Enhanced catalytic performance of Pd‐Ga bimetallic catalysts for 2‐ethylanthraquinone hydrogenation

A series of Pd and Pd‐Ga bimetallic catalysts were prepared by a co‐impregnation method for 2‐ethylanthraquinone (EAQ) hydrogenation to produce hydrogen peroxide. Compared with 0.6Pd catalyst, the hydrogenation efficiency of 0.6Pd1.2Ga catalyst (11.9 g L^?1) increases by 32.2%, and the stability of 0.6Pd1.2Ga catalyst is also higher than that of 0.6Pd catalyst. The structures of the samples were determined by N₂ adsorption–desorption, ICP, XRD, CO chemisorption, TEM, H₂‐TPR, in situ CO‐DRIFTS and XPS. The results suggest that incorporation of Ga species improves Pd dispersion and generates a strong interaction between Ga₂O₃ and Pd interface or between Pd and support. DFT calculation results indicate that the strong adsorption of carbonyl group on Ga₂O₃/Pd interface facilitates the activation of EAQ and promotes the hydrogenation efficiency.     

Selective Hydrogenation of Citral over a Carbon‐titania Composite Supported Palladium Catalyst

A novel carbon‐titania composite material, C/TiO₂, has been prepared by growing carbon nanofibers (CNFs) on TiO₂ surface via methane decomposition using Ni‐Cu as a catalyst. The C/TiO₂ was used for preparing supported palladium catalyst, Pd/C/TiO₂. The support and Pd/C/TiO₂ catalyst were characterized by BET, SEM, XRD and TG‐DTG. Its catalytic performance was evaluated in selective hydrogenation of citral to citronellal, and compared with that of activated carbon supported Pd catalyst. It was found that the Pd/C/TiO₂ catalyst contains 97% of mesopores. And it exhibited 88% of selectivity to citronellal at citral conversion of 90% in citral hydrogenation, which was much higher than that of activated carbon supported Pd catalyst. This result may be attributed to elimination of internal diffusion limitations, which were significant in activated carbon supported Pd catalyst, due to its microporous structure.     

Synthesis,characterization, and application of hollow ceramic microsphere based Pd catalyst for hydrogenation of 2-ethylanthraquinone

Palladium metal has been used extensively in the hydrogenation reactions due to their great affinity towards hydrogen atoms. In the present study, the catalyst preparation attempted with Pd supported Hollow Ceramic Microspheres using wet impregnation method and its use as catalysts is explored in the hydrogenation of 2-ethylanthraquinone studing the effect of the reaction time, temperature, volume of working solution and the catalyst dosages on the conversion of 2-ethylanthraquinone and yield of hydrogen peroxide. The hydrogenation reaction of 2-ethylanthraquinone is the key step in the anthraquinone method for the industrial production of the hydrogen peroxide. The Pd supported catalyst was characterized by XRF, FTIR, and BET to confirm the composition of the prepared catalyst, Pd deposition, and the surface area. The highest catalyst activity was found to be 9.42 ​g/L with the maximum conversion of 96% at 70°C, 0.3 ​MPa. The kinetics of the heterogeneous hydrogenation reaction of 2-ethylanthraquinone with Pd supported on Hollow Ceramic Microspheres as catalyst was also investigated. This paper is in contribution of our earlier publication.     

Carbon nanofiber supported palladium catalyst for liquid-phase reactions: An active and selective catalyst for hydrogenation of cinnamaldehyde into hydrocinnamaldehyde

Carbon nanofibers (CNFs) prepared by decomposition of ethane over a Ni/alumina catalyst, are used as support for palladium clusters. The carbon support displays a mean diameter of 40–50 nm, lengths up to several tens of micrometers, as highlighted by transmission electron microscopy (TEM) observations and a specific surface area of about 50 m²/g. The spheroidal palladium particles have a relatively homogeneous and sharp size distribution, centered at around 4 nm. This novel Pd/carbon nanofiber catalyst displays unusual catalytic properties and is successfully used in the selective hydrogenation of the C=C bond in cinnamaldehyde at a reaction temperature of around 80°C, under continuous hydrogen flowing at atmospheric pressure. The high performances of this novel catalyst in terms of efficiency and selectivity are, respectively, related to the inhibition of the mass-transfer processes over this non-porous material and to peculiar palladium–carbon interactions. It is concluded that the absence of microporosity in the carbon nanofibers favours both the high activity and selectivity which is confirmed by comparison with the commercially available high surface area charcoal supported palladium catalyst.     

Hydrogenation of arenes, alkenes and alkynes catalyzed by a sol–gel entrapped mixture of [Rh(cod)Cl]2 and Na[HRu3(CO)11]

A sol–gel entrapped 1:3 mixture of [Rh(cod)Cl]₂ and Na[HRu₃(CO)₁₁] catalyzes the hydrogenation of various unsaturated substrates by two distinguishable mechanisms. Under 13.8 bar H₂ and 20 °C methylated arenes react rapidly to give cycloalkane derivatives. XRD and TEM studies showed that under these conditions the hydrogenation proceeds without the generation of free metal particles. The hydrogenation of non-methylated arenes, as well as that of alkenes and alkynes, require a temperature of 80–120 °C at which the entrapped complexes form metallic nano-particles of 3–5 nm. Chloroarenes are also hydrodechlorinated at 120 °C, but require a hydrogen pressure of ≥25 bar. At both temperature ranges the catalysts are reusable at least four times. The high efficiency of the hydrogenation process at 20 °C is rationalized by a synergistic effect between the two different metal atoms of the combined catalyst. This may be related to a remote control model through a hydrogen spillover mechanism.     

Cellulosic nanoparticles from alfa fibers (<Emphasis Type="Italic">Stipa tenacissima)</Emphasis>: extraction procedures and reinforcement potential in polymer nanocomposites

The microstructure and chemical composition of alfa (Stipa tenacissima) were investigated. The polysaccharide and lignin contents were around 70 and 20 wt%, respectively. From the bleached and delignified fibers, two types of nanosized cellulosic particles were extracted, namely cellulose nanocrystals and microfibrillated cellulose (MFC). The former correspond typically to the elementary crystallite units of the cellulose fibers, with a rod-like morphology and an aspect ratio of about 20. The latter, mechanically disintegrated from oxidized bleached fibres, presents an entangled fibrillar structure with widths in the range 5-20 nm. The reinforcing potential of the ensuing nanoparticles was investigated by casting a mixture of acrylic latex and aqueous dispersion of cellulose nanoparticles. Thermo-mechanical analysis revealed a huge enhancement of the stiffness above the glass transition of the matrix. Significant differences in the mechanical reinforcing capability of the nanoparticles were reported.     

The effect of surface electrolytic treatment on carbon fibers and the microstructure of pyrocarbon around it during chemical vapor deposition

Before chemical vapor deposition, carbon fibers were electrolyzed for different time, using 33 wt% nitric acid and 5 wt% ammonium bicarbonate solution as electrolyte solution respectively. Effects of the electrolytic treatments on the morphology and chemical functional groups of carbon fibers were deeply analyzed. The influence of these surface treatments on the deposition of pyrocarbon during chemical vapor deposition was also investigated. Results show that the electrolytic treatments for proper time improve the surface morphology and adjust the surface functional groups of carbon fibers. The main functional groups on fiber surface are HBS and –COOH groups, which then induce the efficient deposition of pyrocarbon and improve the microstructure of pyrocarbon during chemical vapor deposition.     

Metal–organic framework derived Pd/ZrO2@CN as a stable catalyst for the catalytic hydrogenation of 2,3,5‐trimethylbenzoquinone

Metal–organic frameworks (MOFs) have recently been identified as versatile sacrificing templates to construct functional nanomaterials for heterogeneous catalysis. Herein, we report a thermal transformation strategy to directly fabricate metal Pd nanoclusters inlaid within a ZrO₂@nitrogen‐doped porous carbon (Pd/ZrO₂@CN) composite using Pd@NH₂‐UiO‐66(Zr) as a precursor that was pre‐synthesized by a one‐pot hydrothermal method. The developed Pd/ZrO₂@CN as a robust catalyst delivered remarkable stability and activity to the catalytic hydrogenation of 2,3,5‐trimethylbenzoquinone (TMBQ) to 2,3,5‐trimethylhydroquinone (TMHQ), a key reaction involved in vitamin E production. The hydrogenation was carried out at 110 °C with 1.0 MPa H₂, and it resulted in 98% TMHQ yield as the sole product over five consecutive cycles, outperforming the analogue Pd/ZrO₂@C without nitrogen doping templated from Pd@UiO‐66(Zr). The excellent catalytic properties of Pd/ZrO₂@CN likely originated from the highly stable ultrafine Pd nanoclusters inlaid within ZrO₂@CN matrix on account of the strong interaction between N and Pd, as well as on the Lewis acidity of ZrO₂, which was beneficial to the hydrogenation.     

Catalytic activity of the VIII Group metals in the hydrogenation and isomerization of α- and β-pinenes

The kinetic regularities of the liquid-phase hydrogenation and isomerization of α- and β-pinenes over the Pd/C, Ru/C, Rh/C, Pt/C, and Ir/C catalysts were studied at temperatures ranging from 20 to 100 °C and at hydrogen pressures of 1–11 bar using n-octane as the solvent. The hydrogenation and isomerization of α- and β-pinenes occur simultaneously on the Ru/C, Rh/C, Pt/C, and Ir/C catalysts, and the reaction mixture contains the products of double bond hydrogenation, viz., cis- and trans-pinanes. The Ru, Rh, and Pd metals have a higher catalytic activity in β-pinene isomerization than Ir and Pt. Among the VIII Group metals studied, the Pd-based catalyst has the highest catalytic activity in double bond isomerization of α- and β-pinenes. The general scheme of the mechanism of hydrogenation and isomerization of α- and β-pinenes on the Pd/C catalyst was proposed.     

Synthesis and acid catalysis of cellulose-derived carbon-based solid acid

SO₃H-bearing amorphous carbon, prepared by partial carbonization of cellulose followed by sulfonation in fuming H₂SO₄, was applied as a solid catalyst for the acid-catalyzed hydrolysis of β-1,4 glucan, including cellobiose and crystalline cellulose. Structural analyses revealed that the resulting carbon material consists of graphene sheets with 1.5 mmol g^?1 of SO₃H groups, 0.4 mmol g^?1 of COOH, and 5.6 mmol g^?1 of phenolic OH groups. The carbon catalyst showed high catalytic activity for the hydrolysis of β-1,4 glycosidic bonds in both cellobiose and crystalline cellulose. Pure crystalline cellulose was not hydrolyzed by conventional strong solid Brønsted acid catalysts such as niobic acid, Nafion^® NR-50, and Amberlyst-15, whereas the carbon catalyst efficiently hydrolyzes cellulose into water-soluble saccharides. The catalytic performance of the carbon catalyst is due to the large adsorption capacity for hydrophilic reactants and the adsorption ability of β-1,4 glucan, which is not adsorbed to other solid acids.