Yves Schuurman

TAP-2: An interrogative kinetics approach

The TAP-2 reactor system and the theoretical basis of TAP pulse response experiments are discussed. On the basis of the TAP system, an alternative to the traditional kinetic approach in heterogeneous catalysis is developed. This new approach, termed ‘interrogative kinetics’ involves a combination of two types of kinetic experiments called ‘state-defining’ (friendly) and ‘state-altering’ (typical) experiments. The state defining kinetic parameter, or ‘kinetic parameter of the catalyst’ (KPC) is proposed and compared with the kinetic characteristic ‘turnover number’. The theory of TAP pulse response experiments is developed. Two deterministic models based on partial-differential equations are analyzed for the cases of diffusion, irreversible adsorption/reaction and reversible adsorption. The ‘standard diffusion curve’ that can be used for distinguishing the Knudsen flow regime is described, and simple criteria of the Knudsen regime are proposed. The concept of relative flow is described, and different fingerprints of TAP kinetics for irreversible adsorption/reaction and reversible adsorption are presented. TAP-2 experimental results on the selective oxidation of n-butane are used to illustrate the methodology of interrogative kinetics.

Heats of adsorption for seven gases in three metal - Organic frameworks: Systematic comparison of experiment and simulation

The heat of adsorption is an important parameter for gas separation and storage applications in porous materials such as metal-organic frameworks (MOFs). There are, however, few systematic studies available in the MOF literature. Many papers report results for only one MOF and often only for a single gas. In this work, systematic experimental measurements by TAP-2 are reported for the heats of adsorption of seven gases in three MOFs. The gases are Kr, Xe, N2, CO2, CH4, n-C4H10, and i-C4H10. The MOFs studied are IRMOF-1, IRMOF-3, and HKUST-1. The data set provides a valuable test for molecular simulation. The simulation results suggest that structural differences in HKUST-1 experimental samples may lead to differing heats of adsorption.

MOF-Supported Selective Ethylene Dimerization Single-Site Catalysts through One-Pot Postsynthetic Modification

The one-pot postfunctionalization allows anchoring a molecular nickel complex into a mesoporous metal-organic framework (Ni@(Fe)MIL-101). It is generating a very active and reusable catalyst for the liquid-phase ethylene dimerization to selectively form 1-butene. Higher selectivity for 1-butene is found using the Ni@(Fe)MIL-101 catalyst than reported for molecular nickel diimino complexes.

From biomass to bio-gasoline by FCC co-processing: effect of feed composition and catalyst structure on product quality

Due to a worldwide demand for biofuels, a need has emerged to develop new processes. Co-processing of bio-oils in refinery units is a promising alternative, especially by Fluid Catalytic Cracking (FCC). In order to promote biofuel production by co-processing a detailed mechanistic study is required based on comparison with pure vacuum gasoil (VGO) processing. Three different porous materials containing micropores and/or mesopores were tested (FCC, HY and HZSM-5). The co-processing of hydrodeoxygenated pyrolysis oil (HDO-oil) with VGO in a lab test FCC unit leads to lower product formation rates than the processing of VGO alone, except for the coke formation and the formation of more unsaturated components (essentially aromatics). The data for both VGO cracking and co-processing follow the published trends with acid site density. These results are explained by the restricted access of the oxygenated molecules into the zeolite pores and coke formation on the outside surface leading to pore blocking. Another key mechanistic feature, explaining the observed effects of co-processing on the product quality, is the competition for the zeolite acid sites between the cracking route and the deoxygenation of the oxygenated components on the outer surface.

Low temperature oxidative dehydrogenation of ethane over catalysts based on group VIII metals

Abstract Unsupported Fe, Co and Ni catalysts are active in the oxidative dehydrogenation of ethane (ODHE) at low temperature. A conversion of 1% is achieved at 585, 438 and 487 K, respectively. The selectivity towards ethylene is found to be ca. 60% at low conversion. As the reaction temperature increases, the selectivity remains nearly constant for Ni whilst it decreases for Fe and Co. This behaviour has been explained by comparing the catalytic properties of Co and Ni towards ethane and ethylene oxidation. The ODHE intrinsic activity sequence (Co>Ni>Fe) is similar to that observed for the homomolecular exchange of oxygen, confirming that these catalysts are in an oxidized state in the course of the ODHE reaction. The study of the reduction and oxidation of unsupported and silica-supported nickel catalysts using magnetic methods has shown that the catalytic activity is not related to the ease of the Ni 2+ Ni 0 transition. TAP experiments carried out over Ni have revealed that the oxygen species involved in the reaction are irreversibly held by the catalyst at 573 K (possibly O − ) from which a reaction mechanism is proposed. Furthermore, this series of experiments have shown that ethane is irreversibly adsorbed and that CO 2 originates from a parallel-consecutive scheme.

A TAP reactor investigation of the oxidative dehydrogenation of propane over a V–Mg–O catalyst

Abstract The oxidative dehydrogenation of propane (ODHP) was studied over an optimised V–Mg–O catalyst at 500°C using the vacuum transient kinetic technique in the temporal-analysis-of-products (TAP) reactor. The only products detected were C3H6 and COx. The experiments reveal that both, propene and carbon oxides are primary reaction products and that COx is also produced by secondary oxidation of propene. Partial and deep oxidation of propane occur at the same surface site but involve different forms of reactive oxygen, associated to different site arrangements: nucleophilic lattice oxygen takes part in the propane partial oxidation to propene, while adsorbed electrophilic oxygen adspecies, originating from the gas-phase oxygen, are involved in the direct deep oxidation process of propane. The secondary oxidation of propene could involve both types of oxygen species. In the absence of gas-phase oxygen, the oxidation state of the catalyst determines the importance of the consecutive propene total oxidation.

Unraveling mechanistic features for the methane reforming by carbon dioxide over different metals and supports by TAP experiments

Abstract Four different catalysts (Ni/SiO2, Ni/Al2O3, Ru/SiO2, Ru/Al2O3) were extensively investigated in the TAP reactor, in order to elucidate the role of the metal and support in the dry reforming of methane. Over nickel, dissociative CH4 adsorption leads to H2 gas and to an accumulation of carbon species on the surface. Dissociative CO2 adsorption takes place giving CO gas and adsorbed oxygen. The latter reacts with carbon, originating from CH4, on the surface to give a second CO molecule in the rate determining step. Over ruthenium, the methane activation is the slowest step and CO2 reacts directly with adsorbed carbon to CO. The surface oxygen accumulation is minimal and therefore, the oxidation hydrogen is suppressed. Whereas, the silica support is rather inert, the alumina support participates in the reaction by delivering oxygen atoms to the metal via hydroxyl groups spill-over. In addition, a strong interaction between gaseous CO/CO2 and oxygenated adspecies is observed on alumina. The reverse water gas shift reaction takes place under the TAP conditions. The different results are discussed in terms of the hydrogen selectivity.

Uses of transient kinetics for methane activation studies

Abstract The use of transient kinetics is reviewed for recent works performed in the wide area of methane valorization. The specific contribution of techniques such as steady-state isotopic transient kinetics, fast temperature transients, TAP reactor studies is illustrated for reactions involving different modes of methane activation and various types of catalysts.

The fate of bio-carbon in FCC co-processing products

A promising alternative to the first generation of bio-fuels is to produce mixed bio- and fossil fuels by co-processing mixtures of biomass pyrolysis oil with crude oil fractions obtained from distillation in a conventional oil refinery. This was demonstrated to be technically feasible for fluid catalytic cracking (FCC), which is the main refinery process for producing gasoline. However, co-processing leads to more coke formation and to a more aromatic gasoline fraction. A detailed understanding is necessary on how the oxygenated moieties effect the reaction mechanism to further improve the process/catalysts. Moreover, for technical and marketing reasons, it is absolutely required to accurately determine the proportion of renewable molecules in the commercialized products. The carbon-14 method (also called radiocarbon or 14C) has been used as the most accurate and powerful method to discriminate fossil carbon from bio-carbon, since fossil fuel is virtually 14C-free, while biofuel contains the present-day “natural” amount of 14C. This technique has shown that not all FCC products share bio-carbon statistically. The coke formed during a FCC cycle and to a lesser extent the gases are found richer in 14C than gasoline. This result gives valuable information on the co-processing mechanism, supporting that the bio-oil oxygenated molecules are processed more easily at the expenses of the crude oil hydrocarbons, favouring the bio-coke and the bio-light gases production.

Use of transient kinetics techniques for studying the methane reforming by carbon dioxide

Abstract State-of-the-art transient kinetic techniques have been used for studying the mechanism of methane reforming into syngas. Steady-state isotopic transient kinetics (SSITK) and temporal analysis of products (TAP) experiments are reported for Ni- and Ru-silica supported reforming catalysts. Qualitative and quantitative data obtained from the transient kinetics are discussed and mechanistic conclusions are proposed.