Ben Gurion University:
Prof. Moti Herskowitz (Head), Prof. Miron V. Landau, Dr. Ronen Berkovich
Prof. Gideon Grader, Prof. Moshe Sheintuch, Dr. Oz Gazit
The group is researching the development of catalysts and catalytic processes for the sustainable and environmentally friendly production of liquid fuels from a variety of feedstock materials, produced by the four other groups.
Conversion of CO2 and H2 into liquid fuels: The basic renewable feedstocks, water, CO2 and solar energy, are transformed to biomass by natural photosynthesis or to H2 and CO by artificial photosynthesis. Additional raw materials – H2, CO, and CO2 – are obtained by the thermal treatment of biomass. In this group, the raw materials H2, CO and CO2 will constitute the feedstock for the production of liquid fuels by catalytic processes. While there is extensive literature on production of fuels from syngas (CO+H2), the production process for liquid fuels from CO2+H2 is only just emerging.
The main challenge here is to develop catalytic processes that are technologically viable, sustainable, and environmentally acceptable.
In particular, there is a need for a highly efficient process for conversion of CO2 and H2 in one step into liquid hydrocarbons at >90% yield, since CO2 is a major component of biomass gasification and since significant amounts of CO2 are available for recycling at power stations. The key to overcoming this challenge lies in the development of highly active and selective catalytic materials. Iron offers the most promising basis for the development of efficient catalysts for this process. Although FexC carbide active phases have excellent potential, current understanding of CO2 hydrogenation on Fe-based catalysts is limited, and this has strongly inhibited the development of this field.
The Blechner group has developed an integrated catalytic system for direct CO2/H2 synthesis of C6+ hydrocarbons. In this system, which comprises Fe0/FeCx core-shell nanoparticles or a Fe0/FeCx nanoparticles assembly, metallic iron Fe0 exists in equilibrium with FexC and FexO; thus the active surface consists of Fe0 and FeCx. The Fe0 part of the surface is responsible for H2 → 2Hads dissociation, and the surface defects (i.e., low coordination surface Fe0 atoms) are responsible for C-O bond dissociation and formation and stabilization of CHx monomers for further polymerization to higher hydrocarbons. The limitations of these heterogeneous catalysts lie in the high temperatures required and the low stability of bulk carbide phases due to sintering of nanocrystals. It is believed that these limitations can be overcome by incorporating them into nanofiber supports that will be prepared by the Grader group using their expertise in sol-gel technology and electrospinning of ceramic and metal nanofibers. Similar effects of sintering prevention were observed in entrapped silver catalyst for the partial methanol oxidation (PMO) to formaldehyde. Preliminary results obtained at the Blechner Center indicate that the use of FexC nanostructured catalytic materials could provide high selectivity to C2+ hydrocarbons at CO2 conversions of ≥30%. CO evolved from artificial photosynthesis can be efficiently converted to a CO2/H2 mixture in a commercial reverse water gas shift process. This mixture will be utilized in the production of fuels with efficient Fe-carbide based catalyst as described above. In parallel, the CO/CO2/H2 mixture will be converted to methanol/ethanol using a novel catalyst developed at the Technion. This will be followed by production of gasoline in a commercial MTG process (methanol) or in a novel condensation-dehydration process (ethanol) developed at BGU.
Production of “Drop-In” Fuels from Non-Food Oils: This development is motivated by the fact that first generation vegetable oils produced from biomass, e.g., biodiesel, cannot be used as “drop-in” fuels (a mixture of hydrocarbons) for transportation. The Blechner group will pursue three routes for deoxygenation (DOx) of bio-oils containing organic oxygen: decarboxylation (removal of CO2), decarbonylation (removal of CO) and hydrodeoxygenation (removal of water). Catalytic materials for efficient DOx processes require transition metals combined with proper surface acidity. To prevent deactivation of the catalysts, operation under hydrogen pressure is necessary. Thus, to increase the DOx efficiency hydro-decarbonylation/hydro-decarboxylation routes that compete with hydrodeoxygenation are used. Formation of heavy solid paraffins (C16–C18) with high melting points is prevented with nanocrystalline zeolite materials with optimal acidity Catalyst Design. The design of the catalysts will be guided by theoretical and computational studies using density functional theory (DFT) and molecular-dynamics (MD) approaches. The Scheintuch group is experienced in such computations. This approach was recently applied to compare multiple solutions domains during CO oxidation on Pt, Pd, Ir , Rh and Ru, and currently the group is studying the processes associated with H2 production from methane [steam reforming (SR), CH4 + H2O →CO + 3H2 and the water gas shift (WGS) reaction, CO + H2O → CO2 + H2 on Fe, Cu, Ni, Co, Rh, Pt[.
Reactor Design: Once a proper catalyst is selected, the reverse WGS reaction poses several problems of reactor design:
(1) Reaction conversion is expedited by excess hydrogen, but only a small conversion of hydrogen is achieved
(2) Equilibrium limited reactions where conversion can be enhanced by water separation
(3) Reactions are exothermic and reversible, requiring ingenious approaches for enthalpy recuperation and for establishing temperature profiles. Some of these issues can be solved by incorporating selective membranes for separation or by using adsorbents. Conversion enhancement of CO2+H2 reactions will be achieved by incorporation of water-selective silico-alumina or zeolitic membranes. Hydrogen-selective membranes will enable operation at excess H2, and separation of H2 without cooling the stream. It will also enable H2 production from water and CO (from photocatalytic CO2 reduction) in the WGS reaction.
The major goals are twofold:
(1) To convert CO2 and H2 into a range of liquid fuels by direct hydrogenation of CO2 to fuels or to materials such as methanol (that can be converted to gasoline by the MTG process)
(2) To develop novel catalytic processes for deoxygenation, isomerization and mild cracking of heavy paraffins from non-food oils to produce high-quality “drop-in” green diesel and jet fuel with minimum hydrogen consumption. These aims will be accomplished by the preparation of novel catalysts, based on methods developed at the Blechner Center and at the Technion, followed by characterization of the catalysts and testing in lab reactors.
(1) The conversion of a mixture of CO2 and H2 to hydrocarbons at selectivity of >90% to C2+ and catalyst stability of >250 h on stream.
(2) The conversion of non-food vegetable oils to green diesel and jet fuel at LHSV≥1 h-1, selectivity of ≥ 80% and catalyst stability of > 500 h on stream with ≤ 15 g of hydrogen/kg of product.
(3) The development of highly efficient iron-based catalysts on a nanofiber matrix by coupling sol-gel and electrospinning technologies.
(4) The development of a methodology for predicting the rates of reactions of interest, using DFT and MD tools and applying it for the most promising catalysts for WGS, reverse WGS and ethanol production reactions.
(5) The construction and testing of a lab-scale reactor, incorporating water-selective and hydrogen-selective membranes, that enable high-conversion CO2+H2 reactions (e.g., reverse WGS and ethanol production) using excess hydrogen. The results will be used for process design and economic evaluation.