Name: tuning the acidity of pt/ cnts catalysts for hydrodeoxygenation of diphenyl ether
Uploaded: 2019-08-17T13:00:00
Description: Watch this Scientific Journal Video about Tuning the Acidity of Pt/ CNTs Catalysts for Hydrodeoxygenation of Diphenyl Ether at JoVE.com

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 reactor...

<ol>
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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>V000191</td>
			<td></td>
		</tr>
		<tr>
			<td>sulphuric acid (98%)</td>
			<td>MERCK</td>
			<td>100748</td>
			<td></td>
		</tr>
		<tr>
			<td>Lithium carbonate (&#62;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, &#8805;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&#8212;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...

Watch this Scientific Journal Video about Tuning the Acidity of Pt/ CNTs Catalysts for Hydrodeoxygenation of Diphenyl Ether at JoVE.com

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 ...

Functionalized carbon nanomaterials using graphene, carbon nanotubes, carbon nanofibers, and the mesoporous carbon materials play an important role in the valorization of biomass due to the tunable porosity, extremely high specific surface area and excellent hydrophobicity. This protocol demonstrates a general method to tune the acidity of solid acid nanosheet modified platinum carbon nanotubes for biomass valorizations. Acidity of the solid acid can be modified by lowering the number of defects, specific area of the carbon nanotube, and types of solid acid nanosheets so that during biomass conversion, the catalyst can be fine-tuned to produce different products depending on different product's requirements.First, immerse one gram of carbon nanotubes or CNTs in 15 milliliters of nitric acid in a 100 milliliter beaker. Sonicate the solution at 25 degrees Celsius for one and a half hours to remove surface impurities and to enhance the anchoring effect of the catalyst. Then, transfer the solution to a 100 milliliter round-bottom flask.Reflux the solution in a mixture of nitric acid and sulfuric acid at 60 degrees Celsius overnight to create surface defects on the CNTs. After cooling to room temperature, filter the solution to obtain the multi-wall carbon nanotube solid. Wash the solid once with deionized water.Dry the solid at 80 degrees Celsius for 14 hours. Next, weigh kilometric amounts of lithium carbonate and metal oxides niobium oxide and tungsten trioxide in the molar ratio of one to one to two. Calcine the solid mixture at 800 degrees Celsius in air for 24 hours, with one intermediate grinding.Following calcination, place 10 grams of the cold lithium niobium tungstate powder in 200 milliliters of a two-molar nitric acid solution at 50 degrees Celsius and stir the solution for five days, with one replacement of the acid every 24 hours. During the five days, exchange the acid liquid every day and repeat the previous step. Filter the solid and wash it with deionized water three times.Then, dry the solid at 80 degrees Celsius overnight. Now, add 25%tetra and butyl ammonium hydroxide solution to 150 milliliters of a deionized water solution containing two grams of the prepared protonated compound, until the pH reaches 9.5 to 10. Then, stir the solution for seven days.After seven days, centrifuge the solution. Collect the supernatant that contains the dispersed nanosheets. Next, weigh kilometric amounts of lithium carbonate and metal oxides niobium oxide and molybdenum trioxide in a molar ratio of one to one to two.Calcine the solid mixture at 800 degrees Celsius in air for 24 hours, with one intermediate grinding. After calcination, place 10 grams of the cooled lithium niobium molybdate powder in 200 milliliters of a two-molar nitric acid solution at 50 degrees Celsius and stir the solution for five days, with one replacement of the acid at 60 hours. Next, weigh kilometric amounts of lithium carbonate and metal oxides tantalum pentoxide and tungsten trioxide in a molar ratio of one to one to two.Calcine the solid mixture at 900 degrees Celsius in air for 24 hours, with one intermediate grinding. Following calcination, place 10 grams of the cooled lithium tantalum tungstate powder in 200 milliliters of a two-molar nitric acid solution at 50 degrees Celsius and stir the solution for five days, with one replacement of the acid at 60 hours. Add two grams of the prepared multi-wall CNTs to a 100 milliliter solution of the niobium tungstic acid nanosheets in a 250 milliliter round-bottom flask.Add 100 milliliters of a one molar nitric acid solution to the round-bottom flask dropwise to aggregate the nanosheet samples. Continue to stir the solution at 50 degrees Celsius for six hours. Following this, filter the solid and wash with deionized water three times.Dry the solid at 80 degrees Celsius overnight. The next day, weigh the dried solid and record the percent floating of the solid acid on the multi-wall CNTs. Prepare a one gram per 100 milliliter solution of chloroplatinic acid and water.Then, impregnate the as prepared nanosheet modified CNTs with 1.34 milliliters of the aqueous platinum solution. After drying the nanosheet CNTs, calcinate in air at 400 degrees Celsius for three hours. Obtain the niobium tantalum-based solid acid nanosheet modified platinum CNT catalysts.Dilute 05 grams of catalysts in five milliliters of quartz sand. Load the solution in the middle of a fixed bed reactor between two pillows of quartz wool. Reduce the catalyst in hydrogen at 300 degrees Celsius for two hours.Pump the diphenyl ether feedstocks into the fixed bed reactor at different flow rates from 05 to 06 milliliters per minute. Collect the products at different space times, defined as the ratio between the mass of catalyst and the flow rate of the substrate. Identify the liquid products, using a gas chromatograph, equipped with a 5977A mass selective detector and analyze offline by gas chromatography.Finally, determine the conversion of reactants'selectivity towards product and yield of product, using the appropriate equations. The x are depattern of the precursor lithium niobium tungstate has three distinctive diffraction peaks, which represent a well ordered layered structure and is in good agreement with the tetragonal orthorhombic phase observed for lithium niobium tungstate. After the protonic exchange reaction, a diffraction peak at 6.8 degrees was observed, which agreed with the patterns observed in niobium tungstic acid and indicates the existence of a layered structure.The x are depattern after exfoliation and mixing with CNTs has peaks attributed to carbons 002 and the 110 and 200 lattice plane of the niobium tungstic acid nanosheets. After exfoliation, the diffraction peak at 6.8 degrees almost entirely disappeared, indicating that the layered compounds were completely transformed into a nanosheet structure. SEM of the platinum impregnated on 20%niobium tungstic acid with carbon nanotubes, and the corresponding elemental mapping analysis of the different elements of the catalysts are shown here.The analysis directly illustrated the distribution of the platinum particles, demonstrating that these particles, as well as niobium and tungsten, are uniformly dispersed on the surface of the catalysts. All the nanosheet modified platinum catalysts have weak acid characteristic sites that are depicted by the peaks centered at 210 degrees Celsius. Two peaks indicating medium acid strength are centered at 360 and 450 degrees Celsius.Don't forget to mix the right ratio of nitric acid and sulfuric acid. And maintain an accurate temperature to ensure reproducibility of surface diffracts creations. Following this procedure, all the methods like preparing catalysts with different metal centres can be performed to answer questions like how to optimize the hydro conversion activity of diphenyl ether and other derived model compacts.After demonstrating that, the as prepared solid acid can convert biomass-derived small molecules, such as diphenyl ether. The next question will be whether this catalyst can be used to convert a real biomass micromolecules to small molecules. This may require the further turning of the acidity of solid catalysts.Don't forget that working with niobium oxide and related mixed metal oxides can be extremely toxic, and precautions should always be taken while handling nitric acid and sulfuric acid. High pressure reactors and

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