Synthesis of Ethanol from Syngas over Rh/MCM-41 Catalyst: Effect of Water on Product Selectivity

Abstract

Abstract: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 °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 C2-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 N2-physisorption, X-ray photoelectron OPEN ACCESSCatalysts 2015, 5 1738 spectroscopy, X-ray diffraction, H2-chemisorption, transmission electron microscopy and temperature programmed reduction.

Efficient Hydrogenolysis of Guaiacol over Highly Dispersed Ni/MCM-41 Catalyst Combined with HZSM-5

“…To characterize the overall concentration and strength of the acid sites on various samples, temperature-programmed desorption of ammonia (NH 3 -TPD) analysis was performed. The NH 3 -TPD spectrum of the tested samples displayed a broad distribution of acid sites with weak and strong strength, shown in Figure 5, and the quantitative data of NH 3 adsorbed for the various samples are shown in Table 2. The low-temperature desorption peak at around 250 • C could correspond to NH 3 absorbed on the weak acid sites derived from surface silanol groups.…”

“…To this purpose, highly ordered mesoporous materials have displayed extensive potential applications in purification and catalysis. Among them, siliceous MCM-41 is regarded as an ideal support for supported metal catalysts due to its large surface area and high porosity, which is able to well disperse the active phase on the surface [2,3]. In order to synthesize Ni-based catalysts with high performance, there are several preparation methods to produce MCM-41 supported Ni catalysts, such as deposition precipitation [4], impregnation [5], ion-exchange [6], in situ incorporation [7], chemical vapor or atomic layer deposition [8], etc.…”

Phthalhydrazide immobilized on MCM‐41 as a potent and recoverable catalyst for the synthesis of pyrrolo[2,1‐a]isoquinolines

“…Generally, MCM‐41 exhibits mild acidity and weak hydrogen bonding, but active catalytic sites can be generated by the incorporation of organic or inorganic species into their structures. Frequently imidazole, piperazine, aluminum atom, boron, and some transition metals such as Zn, Ti, and Fe can be employed to achieve this …”

Surface Chemistry and Catalysis

“…Lopez L. et al [10] comparatively explored the catalytic performance of Rh/MCM-41 and Rh/SiO 2 catalysts for ethanol synthesis from syngas. The obtained differences in activity and selectivity were attributed, on the basis of complementary catalytic and surface characterization studies, to the different concentrations of water vapor in the pores of Rh/MCM-41.…”

“…It consists of 14 high-quality papers, involving: a comprehensive review article on the surface analysis techniques that can be employed to elucidate the phenomenon of electrochemical promotion in catalysis [3]; two theoretical studies (Density Functional Theory, DFT) on H 2 O dissociation and its implications in catalysis [4,5]; two mechanistic studies by means of temperature-programmed desorption/surface reaction (TPD/TPSR) and/or operando spectroscopy on N 2 O formation over NO x storage-reduction (NSR) catalysts [6] and on methanol reforming over cobalt catalysts [7]; two articles on H 2 production by the steam reforming of ethanol [8] or diesel [9] over transition metal-based catalysts; two articles on the production of commercial fuels by Fisher-Tropsch synthesis [10,11]; two articles on Au-catalyzed CO oxidation [12] and preferential CO oxidation [13]; and three experimental investigations regarding the structure-activity correlation of NO oxidation to NO 2 over Mn-Co binary oxides [14], cyclohexene oxidation on TiZrCo mixed oxides [15] and alkene epoxidation on silica nanoparticles [16].…”