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Synthesis of Ethanol from Syngas over Rh/MCM-41 Catalyst: Effect of Water on Product Selectivity
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology. UMSA Universidad Mayor de San Andrés, Bolivia.ORCID iD: 0000-0001-8488-4429
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology. UMSA Universidad Mayor de San Andrés, Bolivia.ORCID iD: 0000-0002-3793-1197
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2015 (English)In: CATALYSTS, ISSN 2073-4344, Vol. 5, 1737-1755 p.Article in journal (Refereed) Published
Resource type
Text
Abstract [en]

The thermochemical processing of biomass is an alternative route for the manufacture of fuel-grade ethanol, in which the catalytic conversion of syngas to ethanol is a key step. The search for novel catalyst formulations, active sites and types of support is of current interest. In this work, the catalytic performance of an Rh/MCM-41 catalyst has been evaluated and compared with a typical Rh/SiO2 catalyst. They have been compared at identical reaction conditions (280 degrees C and 20 bar), at low syngas conversion (2.8%) and at same metal dispersion (H/Rh = 22%). Under these conditions, the catalysts showed different product selectivities. The differences have been attributed to the concentration of water vapor in the pores of Rh/MCM-41. The concentration of water vapor could promote the water-gas-shift-reaction generating some extra carbon dioxide and hydrogen, which in turn can induce side reactions and change the product selectivity. The extra hydrogen generated could facilitate the hydrogenation of a C-2-oxygenated intermediate to ethanol, thus resulting in a higher ethanol selectivity over the Rh/MCM-41 catalyst as compared to the typical Rh/SiO2 catalyst; 24% and 8%, respectively. The catalysts have been characterized, before and after reaction, by N-2-physisorption, X-ray photoelectron spectroscopy, X-ray diffraction, H-2-chemisorption, transmission electron microscopy and temperature programmed reduction.

Place, publisher, year, edition, pages
MDPI AG , 2015. Vol. 5, 1737-1755 p.
Keyword [en]
ethanol, syngas, Rh/MCM-41 catalyst, water vapor
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-180993DOI: 10.3390/catal5041737ISI: 000367535300008Scopus ID: 2-s2.0-84944885472OAI: oai:DiVA.org:kth-180993DiVA: diva2:898193
Funder
Sida - Swedish International Development Cooperation Agency
Note

QC 20160127

Available from: 2016-01-27 Created: 2016-01-26 Last updated: 2016-11-24Bibliographically approved
In thesis
1. Catalytic conversion of syngas to ethanol and higher alcohols over Rh and Cu based catalysts
Open this publication in new window or tab >>Catalytic conversion of syngas to ethanol and higher alcohols over Rh and Cu based catalysts
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The thermochemical process converts almost any kind of biomass to a desired final product, i.e. gaseous or liquid transportation fuels and chemicals. The transportation fuels obtained in this way are renewable biofuels, which are alternatives to fossil fuels. During the last few years, thermochemical plants for the production of bioethanol have been launched and another is under construction. A total of about 290 million liters of ethanol are expected to be processed per year, mostly using municipal solid waste. Considerable efforts have been made in order to find a more selective catalyst for the conversion of biomass-derived syngas to ethanol.

The thesis is the summary of five publications. The first two publications (Papers I and II) review the state of the art of ethanol and higher alcohols production from biomass, as well as the current status of synthetic fuels production by other processes such as the Fischer-Tropsch synthesis. Paper III analyses the catalytic performance of a mesoporous Rh/MCM-41 (MCM-41 is a hexagonal mesoporous silica) in the synthesis of ethanol which is compared to a typical Rh/SiO2 catalyst. Exhaustive catalytic testing including the addition of water vapor and modifying the hydrogen partial pressure in the syngas feed-stream which, in addition to the catalyst characterization (XRD, BET, XPS, chemisorption, TEM and TPR) before and after the catalytic testing, have allowed concluding that some water vapor can be concentrated in the pores of the Rh/MCM-41 catalyst. The concentration of water-vapor promotes the occurrence of the water gas shift reaction, which in turn induces some secondary reactions that change the product distribution, as compared to results obtained from the typical Rh/SiO2 catalyst. These results have been verified in a wide range of syngas conversion levels (1-68 %) and for different catalyst activation procedures (catalyst reduction at 200 °C, 500 °C and no-reduction) as shown in Paper IV. Finally, similar insights about the use of mesoporous catalyst have been found over a Cu/MCM-41 catalyst, shown in Paper V. Also in Paper V, the effect of metal promoters (Fe and K) has been studied; a noticeable increase of ethanol reaction rate was found over Cu-Fe-K/MCM-41 catalyst as compared to Cu/MCM-41. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. 98 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2017:2
Keyword
thermochemical process, ethanol, higher alcohols, mesoporous catalysts, rhodium, copper, metal promoters
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-196808 (URN)978-91-7729-206-7 (ISBN)
Public defence
2017-01-27, Q2, Osquldas väg 10, Våning 2, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Sida - Swedish International Development Cooperation Agency
Note

QC 20161125

Available from: 2016-11-25 Created: 2016-11-22 Last updated: 2017-02-03Bibliographically approved

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