The work described in this paper was fully supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (UGC/FDS25/E09/17). We also gratefully acknowledge the National Natural Science Foundation of China (21373038 and 21403026) for providing analytical instruments for catalyst characterization and fixed bed reactor for catalyst performance evaluation. Dr. Hongxu Qi would like to thank for the Research Assistantship granted by the Research Grants Council of Hong Kong (UGC/FDS25/E09/17).&#160;

CAUTION: For the proper handling methods, properties and toxicities of the chemicals described in this paper, refer to the relevant material safety data sheets (MSDS). Some of the chemicals used are toxic and carcinogenic and special care must be taken. Nanomaterials may potentially pose safety hazards and health effects. Inhalation and skin contact should be avoided. Safety precautions must be exercised, such as performing the catalyst synthesis in the fume hood and catalyst performance evaluation with autoclave reactors. Personal protective equipment must be worn.
1. Pretreatment of CNTs13
<ol>
	<li>Immerse 1.0 g of CNTs into 50 mL of nitric acid in a 100 mL beaker.</li>
	<li>Sonicate the solution at 25 &#176;C for 1.5 h to remove surface impurities and to enhance the anchoring effect of the catalyst.</li>
	<li>Transfer the solution into a 100 mL round bottom flask.</li>
	<li>Reflux the solution in a mixture of nitric acid (65%) and sulfuric acid (98%) at 60 &#176;C for overnight. Set the volume ratio at 3:1. This will create surface defects on the CNTs.</li>
	<li>Filter the solution to obtain the multiwall carbon nanotube solid. Wash the solid with deionized water.</li>
	<li>Dry the solid at 80 &#176;C for 14 h.</li>
</ol>
2. Preparation of HNbWO6 solid acid nanosheets15 by protonic exchange followed by exfoliation
<ol>
	<li>Mix stoichiometric amounts of Li2CO3 (0.9236 g) and metal oxides Nb2O5 (3.3223 g) and WO3 (5.7963 g) at a molar ratio of 1:1:2.</li>
	<li>Calcine the solid mixture at 800 &#176;C for 24 h with one intermediate grinding.</li>
	<li>Place 10.0 g of LiNbWO6 powder in 200 mL of 2 M HNO3 aqueous solution at 50 &#176;C and stir the solution mixture for 5 days (120 h) with one replacement of the acid at 60 h.</li>
	<li>Exchange the acid liquid every day and repeat step 2.3.</li>
	<li>Filter the solid and wash the solid with deionized water 3x.</li>
	<li>Dry the solid at 80 &#176;C overnight.</li>
	<li>Add an amount of 25 wt.% TBAOH (tetra (n-butylammonium) hydroxide) solution to 150 mL of deionized water solution with 2.0 g of protonated compound obtained in step 2.6 until the pH reaches 9.5 &#8211; 10.0.</li>
	<li>Stir the above solution for 7 days.</li>
	<li>Centrifuge the above solution and collect the supernatant solution that contains the dispersed nanosheets.</li>
</ol>
3. Preparation of HNbMO6 solid acid nanosheets
NOTE: The procedure is similar to that of step 2 except for the first and third steps.
<ol>
	<li>Mix stoichiometric amounts of Li2CO3 and metal oxides Nb2O5 and MoO3 in a molar ratio of 1:1:2.</li>
	<li>Calcine the above solid mixtures at 800 &#176;C in air for 24 h with one intermediate grinding.</li>
	<li>Place 10.0 g of LiNbMoO6 powder in 200 mL of 2 M HNO3 aqueous solution at 50 &#176;C and stir the solution mixture for 5 days (120 h) with one replacement of the acid at 60 h.</li>
</ol>
4. Preparation of HTaWO6 solid acid nanosheets
NOTE: The procedure is similar to that of step 2 except for the first and third steps.
<ol>
	<li>Mix stoichiometric amounts of Li2CO3 and metal oxides Ta2O5 and WO3 in a molar ratio of 1:1:2.</li>
	<li>Calcine the above solid mixtures at 900 &#176;C in air for 24 h with one intermediate grinding.</li>
	<li>Place 10.0 g of LiTaWO6 powder in 200 mL of 2 M HNO3 aqueous solution at 50 &#176;C and stir the solution mixture for 5 days (120 h) with one replacement of the acid at 60 h.</li>
</ol>
5. Preparation of HNbWO6/MWCNTs by the nanosheet aggregation method
<ol>
	<li>Add 2.0 g of multiwall CNTs obtained in step 1 to a 100 mL solution of HNbWO6 nanosheets in a 250 mL round bottom flask.</li>
	<li>Add 100 mL of 1.0 M HNO3 aqueous solution into the round bottom flask dropwise. This will aggregate the nanosheets samples.</li>
	<li>Continue to stir the solution at 50 &#176;C for 6 h.</li>
	<li>Filter the solid and wash the solid with deionized water 3x.</li>
	<li>Dry the solid at 80 &#176;C overnight.</li>
	<li>Weigh the dried solid and record the % loading of the solid acid on the MWCNT.</li>
</ol>
6. Preparation of Pt/20HNbWO6/CNTs by the impregnation method
<ol>
	<li>Dissolve the H2PtCl6&#8729;H2O into water (1.0 g/100 mL).</li>
	<li>Impregnate the as-prepared nanosheets modified CNTs materials with 1.34 mL of the above Pt aqueous solution.</li>
	<li>Dry the nanosheets CNTs materials at 80 &#176;C, and calcinate the materials at 400 &#176;C for 3 h.</li>
	<li>Obtain the Nb(Ta)-based solid acid nanosheets modified Pt/CNTs catalysts.</li>
</ol>
7. Hydrodeoxygenation of lignin-derived aromatic ether
NOTE: The chosen lignin-derived aromatic ether is diphenyl ether in this experiment. The chosen lignin-derived aromatic ether is diphenyl ether in this experiment. The activity of Pt/20HTaWO6/CNTs (88.8% conversion, not shown in this paper) is lower than Pt/20HNbWO6/CNTs (99.6%), thus the yield of cyclohexane decreases. Hence, although, higher selectivity of cyclohexane was obtained over Pt/20HTaWO6/CNTs, lower conversion of diphenyl ether limits its utilization. Using appropriate protective equipment and fume hood to perform the reaction using carcinogenic reagents.
<ol>
	<li>Dilute 0.05 grams of catalyst in 5 milliliters of quartz sand. Load the solution in the middle of a fixed bed reactor between two pillows of quartz wool.</li>
	<li>Reduce the catalyst in H2 (40 mL/min) at 300 &#176;C for 2 h.</li>
	<li>Pump the diphenyl ether feedstocks (including 5.0 wt.% reactant in n-decane and 2.0 wt.% n-dodecane as an internal standard for gas chromatography analysis) into the fixed bed reactor at different flow rates (0.05-0.06 mL/min)</li>
	<li>Collect the products at different space times defined as the ratio between the mass of catalyst W (g) and the flow rate of the substrate F (g/min). 
	<img alt="Equation 1" src="/files/ftp_upload/59870/59870eq1.jpg" /></li>
	<li>Identify the liquid products by an GC (HP-5, 30 m x 0.32 mm x 0.25 &#956;m) with 5977A MSD and analyze off-line by gas chromatography (GC 450, FID, FFAP capillary column 30 m x 0.32 mm x 0.25 &#956;m).</li>
	<li>Determine the conversion of reactants (conv.%), selectivity towards product I (Si %), and yield of product i (Yi %) using the following equations: 
	<img alt="Equation 2" src="/files/ftp_upload/59870/59870eq2.jpg" /> (1) 
	<img alt="Equation 3" src="/files/ftp_upload/59870/59870eq3.jpg" /> (2) 
	<img alt="Equation 4" src="/files/ftp_upload/59870/59870eq4.jpg" /> (3)</li>
</ol>

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We have nothing to disclose.

Pretreatment of CNTs with nitric acid does increase the specific surface area (SBET) significantly. Raw CNTs have a specific surface area of 103 m2/g while after treatment, the surface area was increased to 134 m2/g. Therefore, such pretreatment to create defects on the CNT surface will have a positive effect on the specific surface area on the catalysts after solid acid modification and platinum particle impregnation. Since the surface area will decrease after incorporation of nanosheets...

Many industrial processes for the manufacture of chemicals involve the use of aqueous inorganic acid. One typical example is the conventional H2SO4 process for the hydration of cyclohexane to produce cyclohexanol. The process involves a biphasic system, with the cyclohexane being in the organic phase and the cyclohexanol product being in the acidic aqueous phase, thus making the separation process by simple distillation difficult. Apart from difficulty in separation and recovery, inorganic acid is also highly toxic and corrosive to equipment. Sometimes, the use of inorganic acid generates byproducts that will lower the product yield and must be avoided. For example, the dehydration of 2-cyclohexene-1-ol to produce 1,3-cyclohexadiene using H2SO4 will lead to polymerization byproducts1. Thus, many industrial processes shift towards using solid acid catalysts. Various water tolerant solid acids are used to solve the above problem and to maximize the product yields, such as the use of HZSM-5 and Amberlyst-15. The use of high-silica HZSM-5 zeolite has been shown to replace H2SO4 in the production of cyclohexanol from benzene2. Since the zeolite is present in the neutral aqueous phase, the product will go to the organic phase exclusively, thus simplifying the separation process. However, due to Lewis acid-base adduct formation of water molecules to the Lewis acid sites, zeolitic materials still demonstrated lower selectivity due to the presence of inactive sites3. Among all these solid acids, Nb2O5 is one of the best candidates that contain both Lewis and Br&#216;nsted acid sites. The acidity of Nb2O5&#8729;nH2O is equivalent to a 70% H2SO4 solution, due to the presence of the labile protons. The Br&#216;nsted acidity, which is comparable to protonic zeolite materials, are very high. This acidity will turn to Lewis acidity following water elimination. In the presence of water, Nb2O5 forms the tetrahedral NbO4-H2O adducts, which may decrease in Lewis acidity. However, the Lewis acid sites are still effective since the NbO4 tetrahedral still have effective positive charges4. Such phenomenon has been demonstrated successfully in the conversion of glucose into 5-(hydroxymethyl)furfural (HMF) and the allylation of benzaldehyde with tetraallyl tin in water5. Water-tolerant catalysts are thus crucial in biomass conversion in renewable energy applications, especially when the conversions are performed in environmental benign solvents such as water.
Among the many environmental benign solid acid catalysts, functionalized carbon nanomaterials using graphene, carbon nanotubes, carbon nanofibers, mesoporous carbon materials have been playing an important role in the valorization of biomass due to the tunable porosity, extremely high specific surface area, and excellent hydrophobicity6,7. The sulfonated derivatives are particularly stable and highly active protonic catalytic materials. They can either be prepared by incomplete carbonization of sulfonated aromatic compounds8 or by sulfonation of incompletely carbonized sugars9. They have proven to be very efficient catalysts (e.g., for the esterification of higher fatty acids) with activity comparable to the use of liquid H2SO4. Graphenes and CNTs are carbon materials with a large surface area, excellent mechanical properties, good acid resistance, uniform pore size distributions, as well as resistance to coke deposition. Sulfonated graphene has been found to efficiently catalyze the hydrolysis of ethyl acetate10 and bifunctional graphene catalysts has been found to facilitate the one-pot conversion of levullinic acid to &#947;-valerolactone11. Bifunctional metals supported on CNTs are also very efficient catalysts for application in biomass conversion12,13 such as the highly selective aerobic oxidation of HMF to 2,5-diformylfuran over the VO2-PANI/CNT catalyst14.
Taking advantage of the unique properties of Nb2O5 solid acid, functionalized CNTs and bifunctional metal supported on CNTs, we report the protocol for the synthesis of a series of Nb(Ta)-based solid acid nanosheet modified Pt/CNTs with a high surface area by a nanosheet aggregation method. Furthermore, we demonstrated that Pt/20HNbWO6/CNTs, as a result of the synergistic effect of well-dispersed Pt particles and strong acid sites derived from HNbWO6 nanosheets, exhibit the best activity and selectivity in converting lignin-derived model compounds into fuels by hydrodeoxygenation.

<table><tbody><tr><td>Carbon nanotubes (multi-walled)</td><td>Sigma Aldrich</td><td>724769</td><td></td></tr><tr><td>Nitric acid (65%)</td><td>Sigma Aldrich</td><td>&lt;strong&gt;V000191&lt;/strong&gt;</td><td></td></tr><tr><td>sulphuric acid (98%)</td><td>MERCK</td><td>100748</td><td></td></tr><tr><td>Lithium carbonate (&gt;99%)</td><td>Aladdin</td><td>L196236</td><td></td></tr><tr><td>Niobium pentaoxide (99.95%)</td><td>Aladdin</td><td>N108413</td><td></td></tr><tr><td>Tungsten trioxide (99.8%)</td><td>Aladdin</td><td>T103857</td><td></td></tr><tr><td>Molybdenum trioxide (99.5%)</td><td>Aladdin</td><td>M104355</td><td></td></tr><tr><td>Tantalum oxide (99.5%)</td><td>Aladdin</td><td>T104746</td><td></td></tr><tr><td>Chloroplatinic acid hexahydrate, &amp;ge;37.50% Pt basis</td><td>Sigma Aldrich</td><td>206083</td><td></td></tr><tr><td>tetra (n-butylammonium) hydroxide 30-hydrate</td><td>Aladdin</td><td>D117227</td><td></td></tr><tr><td>Diphenyl ether, 98%</td><td>Aladdin</td><td>D110644</td><td></td></tr><tr><td>2-Bromoacetophenone,98%</td><td>Aladdin</td><td>B103328</td><td></td></tr><tr><td>Diethyl ether,99.5%</td><td>Sinopharm</td><td>10009318</td><td></td></tr><tr><td>n-Decane,98%</td><td>Aladdin</td><td>D105231</td><td></td></tr><tr><td>n-Dodecane,99%</td><td>Aladdin</td><td>D119697</td><td></td></tr><tr><td>Autoclave Reactor</td><td></td><td></td><td>CJF-0.05&amp;mdash;0.1L (Dalian Tongda Equipment Technology Development Co., Ltd)</td></tr><tr><td>Tube furnace</td><td></td><td></td><td>SK2-1-10/12 (Luoyang Huaxulier Electric Stove Co., Ltd)</td></tr></tbody></table>

tuning the acidity of pt/ cnts catalysts for hydrodeoxygenation of diphenyl ether

We herein present a method for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid nanosheets, a series of Pt/xHMNO6/CNTs with different solid acid compositions (x = 5, 20 wt%; M = Nb, Ta; N = Mo, W) have been prepared by carbon nanotube pretreatment, protonic exchange, solid acid exfoliation, aggregation and finally Pt particles impregnation. The Pt/xHMNO6/CNTs are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and NH3-temperature programmed desorption. The study revealed that HNbWO6 nanosheets were attached on CNTs, with some edges of the nanosheets being bent in shape. The acid strength of the supported Pt catalysts increases in the following order: Pt/CNTs &#60; Pt/5HNbWO6/CNTs &#60; Pt/20HNbMoO6/CNTs &#60; Pt/20HNbWO6/CNTs &#60; Pt/20HTaWO6/CNTs. In addition, the catalytic hydroconversion of lignin-derived model compound: diphenyl ether using the synthesized Pt/20HNbWO6 catalyst has been investigated.

X-ray diffraction patterns (XRD) have been studied for the precursor LiNbWO6 and the corresponding proton-exchanged catalyst sample HNbWO6 to determine the phase (Figure 1 and Figure 2). NH3-temperature programmed desorption (NH3-TPD) was used to probe the surface acidity of the catalyst samples (Figure 3). Scanning electron microscopy (SEM) with X-ray microanalysis and...

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Tuning the Acidity of Pt/ CNTs Catalysts for Hydrodeoxygenation of Diphenyl Ether

A protocol for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs is presented.

We herein present a method for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid ...

tuning-acidity-pt-cnts-catalysts-for-hydrodeoxygenation-diphenyl

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Chemistry

Acids and Bases

SCIENTISTS IN ACTION

8.9K Views.  Dalian University of Technology. Gefunctionaliseerde koolstofnanomaterialen met behulp van grafeen, koolstofnanobuisjes, koolstofnanovezels en de mesopozische koolstofmaterialen spelen een belangrijke rol in de valorisatie van biomassa als gevolg van de tunable porositeit, extreem hoge specifieke oppervlakte en uitstekende hydrofobeiteit. Dit protocol toont een algemene methode om de zuurgraad van vaste zuur nanosheet gemodificeerde platina koolstof nanobuisjes voor biomassa valorisaties af te stemmen. De zuurgraad van het v...

Video: Tuning the Acidity of Pt/ CNTs Catalysts for Hydrodeoxygenation of Diphenyl Ether

On the Preparation and Testing of Fuel Cell Catalysts Using the Thin Film Rotating Disk Electrode Method

We present a step-by-step tutorial to prepare proton exchange membrane fuel cell (PEMFC) catalysts, consisting of Pt nanoparticles (NPs) supported on a high surface area carbon, and to test their performance in thin film rotating disk electrode (TF-RDE) measurements. The TF-RDE methodology is widely used for catalyst screening; nevertheless, the measured performance sometimes considerably differs among research groups. These uncertainties impede the advancement of new catalyst materials and, consequently, several authors discussed possible best practice methods and the importance of benchmarking.
The visual tutorial highlights possible pitfalls in the TF-RDE testing of Pt/C catalysts. A synthesis and testing protocol to assess standard Pt/C catalysts is introduced that can be used together with polycrystalline Pt disks as benchmark catalysts. In particular, this study highlights how the properties of the catalyst film on the glassy carbon (GC) electrode influence the measured performance in TF-RDE testing. To obtain thin, homogeneous catalyst films, not only the catalyst preparation, but also the ink deposition and drying procedures are essential. It is demonstrated that an adjustment of the ink&#39;s pH might be necessary, and how simple control measurements can be used to check film quality. Once reproducible TF-RDE measurements are obtained, determining the Pt loading on the catalyst support (expressed as Pt wt%) and the electrochemical surface area is necessary to normalize the determined reaction rates to either surface area or Pt mass. For the surface area determination, so-called CO stripping, or the determination of the hydrogen underpotential deposition (Hupd) charge, are standard. For the determination of the Pt loading, a straightforward and cheap procedure using digestion in aqua regia with subsequent conversion of Pt(IV) to Pt(II) and UV-vis measurements is introduced.

Preparing and testing Pt/C fuel cell catalysts is subject to continuous discussion in the scientific community with respect to reproducibility and best practice. With the presented work, we intend to present a step-by-step tutorial to make and test Pt/C catalysts, which can serve as benchmark for novel catalyst systems.

We present a step-by-step tutorial to prepare proton exchange membrane fuel cell (PEMFC) catalysts, consisting of Pt nanoparticles (NPs) supported on a ...

Environment

Temperature-programmed Deoxygenation of Acetic Acid on Molybdenum Carbide Catalysts

Temperature programmed reaction (TPRxn) is a simple yet powerful tool for screening solid catalyst performance at a variety of conditions. A TPRxn system includes a reactor, furnace, gas and vapor sources, flow control, instrumentation to quantify reaction products (e.g., gas chromatograph), and instrumentation to monitor the reaction in real time (e.g., mass spectrometer). Here, we apply the TPRxn methodology to study molybdenum carbide catalysts for the deoxygenation of acetic acid, an important reaction among many in the upgrading/stabilization of biomass pyrolysis vapors. TPRxn is used to evaluate catalyst activity and selectivity and to test hypothetical reaction pathways (e.g., decarbonylation, ketonization, and hydrogenation). The results of the TPRxn study of acetic acid deoxygenation show that molybdenum carbide is an active catalyst for this reaction at temperatures above ca. 300 &#176;C and that the reaction favors deoxygenation (i.e., C-O bond-breaking) products at temperatures below ca. 400 &#176;C and decarbonylation (i.e., C-C bond-breaking) products at temperatures above ca. 400 &#176;C.

Presented here is a protocol for the operation of a micro-scale temperature-programmed reactor for evaluating the catalytic performance of molybdenum carbide during acetic acid deoxygenation.

Temperature programmed reaction (TPRxn) is a simple yet powerful tool for screening solid catalyst performance at a variety of conditions. A TPRxn system ...

Synthesis and Testing of Supported Pt-Cu Solid Solution Nanoparticle Catalysts for Propane Dehydrogenation

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are demonstrated here. The catalyst forms a substitutional solid solution structure, with a small and uniform particle size around 2 nm. This is realized by careful control over the impregnation, calcination, and reduction steps during catalyst preparation and is identified by advanced in situ synchrotron techniques. The catalyst propane dehydrogenation performance continuously improves with increasing Cu:Pt atomic ratio.

A convenient method for the synthesis of 2 nm supported bimetallic nanoparticle Pt-Cu catalysts for propane dehydrogenation is reported here. In situ synchrotron X-ray techniques allow for the determination of the catalyst structure, which is typically unobtainable using laboratory instruments.

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are ...

Multiscale Sampling of a Heterogeneous Water/Metal Catalyst Interface using Density Functional Theory and Force-Field Molecular Dynamics

A significant number of heterogeneously-catalyzed chemical processes occur under liquid conditions, but simulating catalyst function under such conditions is challenging when it is necessary to include the solvent molecules. The bond breaking and forming processes modeled in these systems necessitate the use of quantum chemical methods. Since molecules in the liquid phase are under constant thermal motion, simulations must also include configurational sampling. This means that multiple configurations of liquid molecules must be simulated for each catalytic species of interest. The goal of the protocol presented here is to generate and sample trajectories of configurations of liquid water molecules around catalytic species on flat transition metal surfaces in a way that balances chemical accuracy with computational expense. Specifically, force field molecular dynamics (FFMD) simulations are used to generate configurations of liquid molecules that can subsequently be used in quantum mechanics-based methods such as density functional theory or ab initio molecular dynamics. To illustrate this, in this manuscript, the protocol is used for catalytic intermediates that could be involved in the pathway for the decomposition of glycerol (C3H8O3). The structures that are generated using FFMD are modeled in DFT in order to estimate the enthalpies of solvation of the catalytic species and to identify how H2O molecules participate in catalytic decompositions.

The goal of the protocol presented here is to generate and sample trajectories of configurations of liquid water molecules around catalytic species on a flat transition metal surface. The sampled configurations can be used as starting structures in quantum mechanics-based methods.

A significant number of heterogeneously-catalyzed chemical processes occur under liquid conditions, but simulating catalyst function under such conditions ...

A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis

Heteroarylation introduces heteroaryl fragments to organic molecules. Despite the numerous available reactions reported for arylation via transition metal catalysis, the literature on direct heteroarylation is scarce. The presence of heteroatoms such as nitrogen, sulfur and oxygen often make heteroarylation a challenging research field due to catalyst poisoning, product decomposition and the rest. This protocol details a highly efficient direct &#945;-C(sp3) heteroarylation of ketones under microwave irradiation. Key factors for successful heteroarylation include the use of XPhos Palladacycle Gen. 4 Catalyst, excess base to suppress side reactions and the high temperature and pressure achieved in a sealed reaction vial under microwave irradiation. The heteroarylation compounds prepared by this method were fully characterized by proton nuclear magnetic resonance spectroscopy (1H NMR), carbon nuclear magnetic resonance spectroscopy (13C NMR) and high-resolution mass spectrometry (HRMS). This methodology has several advantages over literature precedents including broad substrate scope, rapid reaction time, greener procedure and operational simplicity by eliminating the preparation of intermediates such as silyl enol ether. Possible applications for this protocol include, but are not limited to, diversity-oriented synthesis for the discovery of biologically active small molecules, domino synthesis for the preparation of natural products and ligand development for new transition metal catalytic systems.

Heteroaryl compounds are important molecules utilized in organic synthesis, medicinal and biological chemistry. A microwave-assisted heteroarylation using palladium catalysis provides a rapid and efficient method to attach heteroaryl moieties directly to ketone substrates.

Heteroarylation introduces heteroaryl fragments to organic molecules. Despite the numerous available reactions reported for arylation via transition metal ...

Catalytic Reactions at Amine-Stabilized and Ligand-Free Platinum Nanoparticles Supported on Titania During Hydrogenation of Alkenes and Aldehydes

Ligands like amines are used in the colloidal synthesis approach to protect platinum nanoparticles (Pt NP&#39;s) from agglomeration. Normally, ligands like amines are removed by diverse pre-treatment procedures before use in heterogeneous catalysis as amines are considered as a catalyst poison. However, a possible beneficial influence of these surface modifiers on hydrogenation reactions, which is known from spectator species on metal surfaces, is often neglected.
Therefore, amine-stabilized Pt nanoparticles supported by titania (P25) were used without any pre-treatment in order to elucidate a possible influence of the ligand in liquid phase hydrogenation reactions. The catalytic activity of amine-stabilized Pt nanoparticles of two different sizes was investigated in a double-walled stirring tank reactor at 69 &#176;C to 130 &#176;C and 1 atm hydrogen pressure. The conversion of cyclohexene to cyclohexane was determined by gas chromatography (GC) and was compared to ligand-free Pt particles. All catalysts were checked before and after reaction by transmission electron spectroscopy (TEM) and X-ray photoelectron spectroscopy (XPS) for possible changes in size, shape, and ligand shell. The hydrogenation of cyclohexene in liquid phase revealed a higher conversion for amine-stabilized Pt nanoparticles on titania than the ligand-free particles. The hydrogenation of 5-methylfurfural (5-MF) was chosen for a further test reaction, since the hydrogenation of &#945;, &#946;-unsaturated aldehydes is more complex and exhibits various reaction paths. However, XPS and infrared spectroscopy (IR) proved that 5-MF acts as catalyst poison at the given reaction conditions.

This protocol shows a convenient method for comparing the catalytic properties of supported platinum catalysts, synthesized by deposition of nanosized colloids or by impregnation. The hydrogenation of cyclohexene serves as a model reaction to determine the catalytic activity of the catalysts.

Ligands like amines are used in the colloidal synthesis approach to protect platinum nanoparticles (Pt NP&#39;s) from agglomeration. Normally, ligands ...

Hydrogenation

Source: Vy M. Dong and Zhiwei Chen, Department of Chemistry, University of California, Irvine, CA
This experiment will demonstrate the hydrogenation of chalcone as an example of an alkene hydrogenation reaction (Figure 1). In this experiment, palladium on carbon (Pd/C) will be used as a heterogeneous catalyst for the process. A balloon will be used to supply the hydrogen atmosphere.
<img alt="Figure 1" src="/files/ftp_upload/10350/10350fig1.jpg" /> 
Figure 1: Diagram showing the hydrogenation of chalcone to 3-phenylpropiophenone.

Catalytic Hydrogenation of Alkene: Applications in Chemistry

Source: Vy M. Dong and Zhiwei Chen, Department of Chemistry, University of California, Irvine, CA
This experiment will demonstrate the hydrogenation of ...

JoVE Science Education

Organic Chemistry II

Catalytic Reactor: Hydrogenation of Ethylene

Source: <a href="https://www.jove.com/author/Kerry+M._Dooley">Kerry M. Dooley</a> and Michael G. Benton, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA
The hydrogenation of ethylene (C2H4) to ethane (C2H6) has often been studied as a model reduction reaction in characterizing new metal catalysts.1-2 While supported nickel is not the most active metal catalyst for this reaction, it is active enough that reaction can take place at &#60; 200&#176;C.
The reaction typically involves adsorbed, dissociated hydrogen (H2) reacting with adsorbed ethylene. In other words, both hydrogen-atoms and ethylene molecules form bonds with a metal site (here denoted &#34;S&#34;). The strong bonding of ethylene with S weakens the double bond sufficiently to allow hydrogen atoms to add to ethylene, forming ethane, which is not adsorbed.
The purpose of this experiment is, first, to convert raw composition measurements to limiting reactant fractional conversions.3 These conversions can then be used in a plug-flow reactor (PFR) to fit the data to a standard power-law kinetics model by the &#34;Integral Method&#34;.3 A comparison of the experimental orders of reaction for both ethylene and hydrogen with the theoretical orders reveals in this case that the reaction is kinetically controlled rather than mass-transfer controlled.

Heterogeneous Catalytic Reactor and Hydrogenation of Ethylene

Source: Kerry M. Dooley and Michael G. Benton, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA
The hydrogenation of ...

Engineering

Chemical Engineering

Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

<h4>Introduction</h4>
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
<img alt="Figure1" src="/files/ftp_upload/11841/PT_Figure_1.svg" style="text-align: center; height: 100px;" />
<h4>Thermodynamic Stability</h4>
Catalytic hydrogenation reactions help evaluate the relative thermodynamic stability of hydrocarbons. For example, the heat of hydrogenation of acetylene is &#8722;176 kJ/mol, and that of ethylene is &#8722;137 kJ/mol. The higher exothermicity associated with the addition of hydrogen to acetylene suggests that it is thermodynamically less stable than ethylene.
<img alt="Figure2" src="/files/ftp_upload/11841/PT_Figure_2.svg" style="text-align: center; height: 45px;" />
<img alt="Figure3" src="/files/ftp_upload/11841/PT_Figure_3.svg" style="text-align: center; height: 45px;" />
<h4>Modified Catalyst</h4>
Catalytic reduction of alkynes can be stopped at the cis-alkene stage using a modified or poisoned catalyst such as Lindlar or P-2 catalyst. The Lindlar catalyst consists of palladium metal deposited on calcium carbonate and modified using lead acetate and quinoline; the P-2 catalyst is a nickel-boride complex.
<img alt="Figure4" src="/files/ftp_upload/11841/PT_Figure_4.svg" style="text-align: center; height: 100px;" />
A modified catalyst lowers the activation energy for the reduction of the first &#960; bond; however, it is not powerful enough to catalyze the reduction of the second &#960; bond. For example, hydrogenation of 2-pentyne over Lindlar catalyst gives cis-2-pentene.
<img alt="Figure5" src="/files/ftp_upload/11841/PT_Figure_5.svg" style="text-align: center; height: 95px;" />
<h4>Hydroboration-Protonolysis</h4>
Hydroboration-protonolysis is a non-catalytic method for the conversion of internal alkynes into cis-alkenes. The reaction involves treating an internal alkyne with borane to form a trialkenylborane intermediate followed by treatment with acetic acid to yield the desired cis-alkene.
<img alt="Figure6" src="/files/ftp_upload/11841/PT_Figure_6.svg" style="text-align: center; height: 150px;" />

Catalytic Hydrogenation of Alkynes: Formation of cis-Alkenes

Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves ...

Organic Chemistry

Unit 1

Alkynes

KEY TERMS AND CONCEPTS

Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an asymmetric hydrogenation process using chiral homogeneous catalysts. The chiral catalysts are designed such that the metal coordinates to a chiral ligand. The most frequently used chiral ligand is BINAP [(2,2&#39;-bis(diphenylphosphino)-1,1&#39;-binaphthyl] &#8212; a chelating diphosphine. The metal coordinates to the two phosphorus atoms of BINAP, creating a chiral environment for itself. Such chiral catalysts have tremendous applications in pharmaceutical industries, such as the asymmetric synthesis of (S)-naproxen, an anti-inflammatory drug molecule, and the synthesis of L-dopa, a drug used to treat patients with Parkinson&#39;s disease.
Asymmetric hydrogenation is specific to the type of double bond undergoing reduction. The presence of a functional group directly adjacent to the target double bond is essential for the hydrogenation process as it aids with effective coordination of the metal.

Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of ...

Tuning the Acidity of Pt/ CNTs Catalysts for Hydrodeoxygenation of Diphenyl Ether

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