Reciprocal Relations Between Kinetic Curves

We study coupled irreversible processes. For linear or linearized kinetics with microreversibility, $\dot{x}=Kx$, the kinetic operator $K$ is symmetric in the entropic inner product. This form of Onsager's reciprocal relations implies that the shift in time, $\exp (Kt)$, is also a symmetric operator. This generates the reciprocity relations between the kinetic curves. For example, for the Master equation, if we start the process from the $i$th pure state and measure the probability $p_j(t)$ of the $j$th state ($j\neq i$), and, similarly, measure $p_i(t)$ for the process, which starts at the $j$th pure state, then the ratio of these two probabilities $p_j(t)/p_i(t)$ is constant in time and coincides with the ratio of the equilibrium probabilities. We study similar and more general reciprocal relations between the kinetic curves. The experimental evidence provided as an example is from the reversible water gas shift reaction over iron oxide catalyst. The experimental data are obtained using Temporal Analysis of Products (TAP) pulse-response studies. These offer excellent confirmation within the experimental error.Comment: 6 pages, 1 figure, the final versio

3D-printing of metallic honeycomb monoliths as a doorway to a new generation of catalytic devices: the Ni-based catalysts in methane dry reforming showcase

Stainless-steel honeycomb monoliths (square cell-shape/230 cpsi cylinders) were 3D-printed and used as support of a Ni/CeO2-ZrO2 powder deposited by washcoating. The resulting catalysts were characterized by XRF, SEM-EDX and H-2-TPR, and tested in the dry reforming of methane reaction. In the 750-900 degrees C range, they showed competitive conversions (45-95%) and H-2/CO ratio (0.84-0.94) compared to cordierite honeycombs with same catalyst loading and geometric characteristics, but did not require activation time thanks to better heat transfer. Both structured catalysts were stable in prolonged TOS experiments. The bare metallic monoliths exhibited significant activity at 900 degrees C due to their intrinsic nickel content

Hydrogen Production from methane steam reforming in a periodically operated reactor for low-temperature fuel cell

Fuel cell technology has experienced rapid development in recent year for both stationary and vehicle applications. PEM fuel cells hold a considerable potential for replacing conventional internal combustion energy in the transportation sector. This type of fuel cell is operated with hydrogen coming from various sources. Currently, steam reforming, partial oxidation and auto-thermal reforming of hydrocarbons are the major routes for hydrogen generation, but all these methods produce a large amount of CO as byproduct with hydrogen. As a novel alternative to those conventional technologies, methane steam reforming base on the iron redox cycle is a process which was designed to convert hydrocarbons to hydrogen with a quality that fulfills the requirements for all fuel cells types. This two-step process is operating in one single reactor without any additional post-processing of the gas as water gas shift and/or preferential oxidation. The technology is based on the cyclic reduction and oxidation of iron oxides. During the first step, the methane reduces the iron oxide to iron. On the second step steam is used as oxidant for production hydrogen. The produced gas consists of steam and CO-free hydrogen that could be supplied directly to PEMFC