Title : Design of efficient and stable structured catalysts for biofuels transformation into syngas by using advanced technologies of nanocomposite active components synthesis, supporting on heat conducting substrates and sintering
Abstract:
Design of efficient, inexpensive and stable to coking catalysts for transformation of biofuels into syngas and hydrogen is a vital problem of sustainable and renewable energy field. This work presents results of extensive research aimed at design and characterization of such structured catalysts performance in transformation of a variety of biofuels (ethanol, acetone, ethyl acetate, anisole, glycerol, sunflower oil, turpentine oil). Nanocomposite active components were comprised of nanoparticles of metals/alloys (Ni, Co, Pt, Ni+Pt, Ni+Ru) supported on the surface of perovskites (La1-xPrxMn1-yCryO3-d, CaTiO3), fluorite Ln-Ce-Zr-O (Ln = La, Pr, Sm), spinel MnxCr3-xO4 and Ruddlesden-Popper (doped Pr2NiO4) oxides with a high lattice oxygen mobility and reactivity (both bulk oxides, their nanocomposites and layers on Fe, Cr, Ti-doped mesoporous MgAl2O4 oxides) prepared by variety of sophisticated methods including supercritical fluids, self-assembly and Pechini routes. The real/atomic structure of nanomaterials was characterized by modern structural and spectral methods, while oxygen mobility was studied by C18O2 isotope heteroexchange, and surface reactivity -by H2 TPR. Co-existence of several channels of oxygen migration in these systems with diffusion coefficients differing by several orders of magnitude was demonstrated with fast channels corresponding to interfaces in nanocomposites, grain boundaries enriched by some cations as well as to cooperative mechanism of oxygen migration in oxides with asymmetric structures such as Ruddlesden-Popper one. Pulse and transient kinetic studies revealed that mechanism of fuels reforming on these types of catalysts can be described by a bifunctional red-ox scheme. Strong metal-support interaction and oxygen mobility provide stability of metal alloy nanoparticles to sintering and coking. Active components were loaded on structured substrates (Ni-Al, SiC, Si-Al-O foams; Fe-Cr-alloy foils, gauzes and microchannel platelets with protective corundum or La2Zr2O7 - LaAlO3 layers sintered by e-beam; microchannel FeAl(O) cermets) from suspensions with addition of surfactants and (Ce,Pr)ZrOx binders, total loading up to 10-20 wt.%. They were sintered by microwave and e-beams using an ILU-6 accelerator. In pilot tests in real concentrated feeds of structured catalysts with optimized active components and substrates, a high yield of syngas was demonstrated approaching equilibrium at ~ 700-800 oC in steam, dry, partial oxidation and mixed reforming of biofuels at short (~0.2 s) contact times, main by-products being CH4 due to cracking and C2H4 due to dehydration. Suppression of the surface acidity and O2 addition to the feed decrease C2H4 content, thus preventing coking even for such fuels as sunflower and turpentine oils. Stable performance was confirmed for more than 200 h time-on-stream. Mathematical modelling demonstrated absence of any heat transfer limitations due to a high thermal conductivity of substrates. No spallation or cracking of the active component layers supported on substrates was revealed. In pilot reactors for the autothermal reforming of the mixtures of natural gas and biofuels equipped with the heat exchangers to warm the inlet feed, a high yield of syngas approaching equilibrium was obtained even at the inlet temperatures not exceeding 100 oC, thus demonstrating a high energy efficiency of their operation. Support by the Russian Science Foundation grant 23-73-00045 is gratefully acknowledged
