Surface-Treated Activated Carbons as Catalysts for the Dehydration and Dehydrogenation Reactions of Ethanol

Quantifying Carbon Active Sites Chemisorbing Hydrogen on Oxygen Containing Activated Carbons during Heat Treatment in Hydrogen Atmosphere

Carbon edge sites have been widely studied because of their importance in surface reactivity and electronic properties. The surface chemistry of the carbon edge sites is relevant to various reactions, and carbon active sites are key topics in many applications. Temperature-programmed desorption (TPD) and temperature-programmed reaction (TPR) techniques are used to clarify the fate of oxygen atoms present as CO-yielding functional groups on the activated carbon during heat treatment in hydrogen with an argon balance atmosphere. It has been elucidated that CO is decomposed, H2O is released by a reduction reaction with atmospheric H2, and CO2 is evolved by secondary reactions from the CO-yielding functional groups during TPR. Atmospheric H2 consumption during TPR is observed and its rate is characterized. The amounts of carbon active sites are quantified by determining the amount of H2 chemisorbed onto the carbon surfaces. Finally, it is quantitatively determined that the active sites that chemisorb hydrogen are generated after the decomposition of CO and CO2 caused by secondary reactions between ca. 700 and 1100 K from the CO-yielding functional groups. The origin of these CO-yielding functional groups is generally attributed to phenol/ether groups. In addition to these oxygen-containing functional group decompositions, some free sites on the edge sites are activated for H2 chemisorption by heat treatment between ca. 700 and 1100 K.

Synthesis of Oxygenated Hydrocarbons from Ethanol over Sulfided KCoMo-Based Catalysts: Influence of Novel Fiber- and Powder-Activated Carbon Supports

Ethanol has become a viable feedstock for basic organic synthesis. The catalytic conversion of ethanol provides access to such chemicals as diethyl ether, ethyl acetate, and acetaldehyde. Carbonaceous materials are extensively studied as supports for heterogeneous catalysts due to their chemical and thermal stability, high surface area, and tunable texture. In this paper, ethanol conversion over K10Co3.7Mo12S-catalysts supported on novel activated carbon (AC) materials (i.e., novel powder-AC (DAS and YPK-1), fiber non-woven AC material (AHM), and fabric active sorption (TCA)) was investigated. The catalysts were prepared by the incipient wetness co-impregnation method followed by sulfidation. The catalysts were characterized by employing N2 adsorption–desorption measurements, TEM, SEM/EDX, UV–Vis spectroscopy, and XRF. Catalytic performance was assessed in a fixed-bed down-flow reactor operating at 320 °C, 2.5 MPa, and with continuous ethanol feeding in an He atmosphere. Activity is highly dependent on the support type and catalyst’s textural properties. The activity of the fiber-supported catalysts was found to be greater than the powder-supported catalysts. Ethanol conversion at T = 320 °C, P = 2.5 MPa, and GHSV = 760 L h−1 kgcat−1 increased as follows: (38.7%) KCoMoS2/YPK-1 < (49.5%) KCoMoS2/DAS < (58.2%) KCoMoS2/TCA < (67.1%) KCoMoS2/AHM. Catalysts supported by powder-AC enhanced the formation of MoS2-crystallites, whereas the high acidity of fiber-AC seemed to inhibit the formation of MoS2-crystallites. Simultaneously, a high surface area and a microporous catalytic structure enhance the formation of oxygenates from hydrocarbons. The dehydration and dehydrogenation reactions, which led to the creation of ethene and acetaldehyde, were shown to require a highly acidic catalyst, while the synthesis of ethyl acetate and higher alcohols required a less acidic catalyst.

Acid Mesoporous Carbon Monoliths from Lignocellulosic Biomass Waste for Methanol Dehydration

Activated carbon monoliths (ACMs), with 25 cells/cm², were prepared from the direct extrusion of Alcell, Kraft lignin and olives stones particles that were impregnated with phosphoric acid, followed by activation at 700 °C. These ACMs were used as catalysts for methanol dehydration reaction under air atmosphere. ACM that was prepared from olive stone and at impregnation ratio of 2, OS2, showed the highest catalytic activity, with a methanol conversion of 75%, a selectivity to dimethyl ether (DME) higher than 90%, and a great stability under the operating conditions studied. The results suggest that the monolithic conformation, with a density channel of 25 cells/cm² avoid the blockage of active sites by coke deposition to a large extent. Methanol conversion for OS2 was reduced to 29% in the presence of 8%v water, at 350 °C, although the selectivity to DME remained higher than 86%. A kinetic model of methanol dehydration in the presence of air was developed, while taking into account the competitive adsorption of water. A Langmuir-Hinshelwood mechanism, whose rate-limiting step was the surface reaction between two adsorbed methanol molecules, represented the experimental data under the conditions studied very well. An activation energy value of 92 kJ/mol for methanol dehydration reaction and adsorption enthalpies for methanol and water of −12 and −35 kJ/mol, respectively, were obtained.

Carbon-Based Catalyst from Pyrolysis of Waste Tire for Catalytic Ethanol Dehydration to Ethylene and Diethyl Ether

This work investigated the use of waste tire as a source of carbon in preparation of carbon-based catalysts for applying in ethanol dehydration. The pyrolysis of waste tire was performed to obtain the solid carbon, and then it was treated with two different acids including HCl and HNO3 prior to the activation process with different temperatures to gain suitable carbon catalysts. All carbon catalysts were characterized using nitrogen physisorption, XRD, FTIR, and acid-base titration. The catalysts were tested for catalytic ethanol dehydration in a micropacked-bed reactor under the temperature range from 200°C to 400°C. It revealed that the ethanol conversion increased with increasing the reaction temperature for all catalysts. The carbon catalyst treated with HCl and calcined at 420°C (AC_H420) exhibited the highest ethanol conversion of 36.2% at 400°C having ethylene and diethyl ether selectivity of 65.9 and 33.5%, respectively. The high activity of this catalyst can be attributed to the high acid density at the surface (18.5 μmol/m2), which was significantly higher than those of most other catalysts (less than 8.0 μmol/m2).

Dehydrogenation of Ethanol to Acetaldehyde over Different Metals Supported on Carbon Catalysts

Recently, the interest in ethanol production from renewable natural sources in Thailand has been receiving much attention as an alternative form of energy. The low-cost accessibility of ethanol has been seen as an interesting topic, leading to the extensive study of the formation of distinct chemicals, such as ethylene, diethyl ether, acetaldehyde, and ethyl acetate, starting from ethanol as a raw material. In this paper, ethanol dehydrogenation to acetaldehyde in a one-step reaction was investigated by using commercial activated carbon with four different metal-doped catalysts. The reaction was conducted in a packed-bed micro-tubular reactor under a temperature range of 250–400 °C. The best results were found by using the copper doped on an activated carbon catalyst. Under this specified condition, ethanol conversion of 65.3% with acetaldehyde selectivity of 96.3% at 350 °C was achieved. This was probably due to the optimal acidity of copper doped on the activated carbon catalyst, as proven by the temperature-programmed desorption of ammonia (NH3-TPD). In addition, the other three catalyst samples (activated carbon, ceria, and cobalt doped on activated carbon) also favored high selectivity to acetaldehyde (>90%). In contrast, the nickel-doped catalyst was found to be suitable for ethylene production at an operating temperature of 350 °C.

Multi-Walled Carbon Nanotubes as a Catalyst for Gas-Phase Oxidation of Ethanol to Acetaldehyde

Multi-walled carbon nanotubes (CNTs) were directly used as a sustainable and green catalyst to convert ethanol into acetaldehyde in the presence of molecular oxygen. The C=O groups generated on the nanocarbon surface were demonstrated as active sites for the selective oxidation of ethanol to acetaldehyde. The transformation of disordered carbon debris on the CNT surface to ordered graphitic structures induced by thermal-treatment significantly enhanced the stability of the active C=O groups, and thus the catalytic performance. A high reactivity with approximately 60 % ethanol conversion and 93 % acetaldehyde selectivity was obtained over the optimized CNT catalyst at 270 °C. More importantly, the catalytic performance was quite stable even after 500 h, which is comparable with a supported gold catalyst. The robust catalytic performance displayed the potential application of CNTs in the industrial catalysis field.

Fabrication of nitrogen-modified annealed nanodiamond with improved catalytic activity

Annealed ultradispersed nanodiamond (ADD) with sp(2) curved concentric graphitic shells is an interesting hybrid material consisting of the remarkable surface properties of graphene-based nanomaterials and the intrinsic properties of a diamond core. In this case, based on its specific properties and surface oxygen functional groups, nitrogen-modified ADD powders have been tunably synthesized via three different preparation methods in a calcination treatment process. The detailed formation and dynamic behaviors of the nitrogen species on the modified ADD during the preparation process are revealed by elemental analysis, X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption. Moreover, we study the catalytic performance on the metal-free nitrogen-modified ADD catalysts by means of selective oxidation of benzylic alcohols as a probe reaction. The results indicate that the modified ADD catalysts exhibit a higher catalytic activity than pristine ADD. By correlating XPS data with catalytic measurements, we conclude that the pyridinic nitrogen species plays a pivotal role in the catalytic reaction. Our work provides valuable information on the design of modified carbon materials with more excellent properties.

Chemocatalytic conversion of ethanol into butadiene and other bulk chemicals

The development of new and improved processes for the synthesis of bio-based chemicals is one of the scientific challenges of our time. These new discoveries are not only important from an environmental point of view, but also represent an important economic opportunity, provided that the developed processes are selective and efficient. Bioethanol is currently produced from renewable resources in large amounts and, in addition to its use as biofuel, holds considerable promise as a building block for the chemical industry. Indeed, further improvements in production, both in terms of efficiency and feedstock selection, will guarantee availability at competitive prices. The conversion of bioethanol into commodity chemicals, in particular direct 'drop-in' replacements is, therefore, becoming increasingly attractive, provided that the appropriate (catalytic) technology is in place. The production of green and renewable 1,3-butadiene is a clear example of this approach. The Lebedev process for the one-step catalytic conversion of ethanol to butadiene has been known since the 1930s and has been applied on an industrial scale to produce synthetic rubber. Later, the availability of low-cost oil made it more convenient to obtain butadiene from petrochemical sources. The desire to produce bulk chemicals in a sustainable way and the availability of low-cost bioethanol in large volumes has, however, resulted in a renaissance of this old butadiene production process. This paper reviews the catalytic aspects associated with the synthesis of butadiene via the Lebedev process, as well as the production of other, mechanistically related bulk chemicals that can be obtained from (bio)ethanol.

Influence of activated carbon modifications on their catalytic activity in methanol and ethanol conversion reactions

Activated carbons containing different surface functionalities have been investigated as catalysts in conversion reactions of ethanol and methanol. These carbon materials were prepared from Polish brown coal by chemical activation with potassium hydroxide and modified by the oxidation or reaction with ammonia or chlorine. The main process upon ethanol decomposition was its dehydrogenation, while in the process of methanol decomposition only a few samples were catalytically active, and the only product was dimethyl ether (a product of dehydration).

Design of low-temperature Pt-carbon combustion catalysts for VOC's treatments

Two series of Pt/C-catalysts were prepared using pure carbon aerogels as supports. The influence of porosity, surface chemistry and Pt dispersion on the activity of Pt/C combustion catalysts was analyzed. The synthesis of the supports was fitted to have a monomodal pore size distribution in the meso and macropore range respectively. Both supports were functionalized by oxidation treatment with H(2)O(2) or (NH(4))(2)S(2)O(8). These treatments did not modify the porosity significantly, but the surface chemistry changed from basic to acid as oxygen content increased. In this way, Pt-dispersion decreased as a result of the low thermal stability of surface carboxylic acid groups. Benzene was selected as target VOCs and the catalytic combustion performance depended mainly on the porous texture and Pt-dispersion, while the variations in the surface chemistry of carbon supports due to oxidation treatments seemed to have a weak influence on this kind of reaction.