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The hydrogenation of CO2 to methanol over Cu/ZnO-based catalysts is highly sensitive to the surface composition and catalyst structure. Thus, its optimization requires a deep understanding of the influence of the pre-catalyst structure on its evolution under realistic reaction conditions, including the formation and stabilization of the most active sites. Here, the role of the pre-catalyst shape (cubic vs spherical) in the activity and selectivity of ZnO-supported Cu nanoparticles was investigated during methanol synthesis. A combination of ex situ, in situ, and operando microscopy, spectroscopy, and diffraction methods revealed drastic changes in the morphology and composition of the shaped pre-catalysts under reaction conditions. In particular, the rounding of the cubes and partial loss of the (100) facets were observed, although such motifs remained in smaller domains. Nonetheless, the initial pre-catalyst structure was found to strongly affect its subsequent transformation in the course of the CO2 hydrogenation reaction and activity/selectivity trends. In particular, the cubic Cu particles displayed an increased activity for methanol production, although at the cost of a slightly reduced selectivity when compared to similarly sized spherical particles. These findings were rationalized with the help of density functional theory calculations.

Supported nickel nanoparticles are promising catalysts for the methanation of CO2. The role of nickel particle size on activity and selectivity in this reaction is a matter of debate. We present a study of metal particle size effects on catalytic stability, activity and selectivity, using nickel on graphitic carbon catalysts. Increasing the Ni particle size from 4 to 8 nm led to a higher catalytic activity, both per gram of nickel and normalized surface area. However, the apparent activation energy remained the same (∼105 kJ mol−1). Comparing experiments at atmospheric to 30 bar pressure demonstrates the importance of testing under industrially relevant pressures; the highest selectivity is obtained at high CO2 conversions and pressures. Finally, the selectivity was particle size-dependent. The largest particles were not only most active but also most selective to methane. With this work we contribute to the ongoing debate about Ni particle size effects in CO2 methanation.

Converting CO2 into value-added chemicals and fuels, such as methanol, is a promising approach to limit the environmental impact of human activities. Conventional methanol synthesis catalysts have shown limited efficiency and poor stability in a CO2/H2 mixture. To design improved catalysts, crucial for the effective utilization of CO2, an in-depth understanding of the active sites and reaction mechanism is desired. The catalytic performance of a series of carbon-supported Cu catalysts, with Cu particle sizes in the range of 5 to 20 nm, was evaluated under industrially relevant temperature and pressure, i.e. 260 °C and 40 bar(g). The CO2 hydrogenation reaction exhibited clear particle size effects up to 13 nm particles, with small nanoparticles having the lower activity, but higher methanol selectivity. MeOH and CO formation showed a different size-dependence. The TOFCO increased from 1.9 × 10−3 s−1 to 9.4 × 10−3 s−1 with Cu size increasing from 5 nm to 20 nm, while the TOFMeOH was size-independent (8.4 × 10−4 s−1 on average). The apparent activation energies for MeOH and CO formation were size-independent with values of 63 ± 7 kJ mol−1 and 118 ± 6 kJ mol−1, respectively. Hence the size dependence was ascribed to a decrease in the fraction of active sites suitable for CO formation with decreasing particle size. Theoretical models and DFT calculations showed that the origin of the particle size effect is most likely related to the differences in formate coverage for different Cu facets whose abundancy depends on particle size. Hence, the CO2 hydrogenation reaction is intrinsically sensitive to the Cu particle size.

Data, scripts and generated microkinetic models for the preprint "Detailed microkinetics for the oxidation of exhaust gas emissions through automated mechanism generation" &nbsp

The side-chain mechanism of the methanol-to-olefins process over the H-SSZ-13 acidic zeolite was investigated using periodic density functional theory with corrections from highly accurate ab intio calculations on large cluster models. Hexa-, penta- and tetramethylbenzene are studied as co-catalysts for the production of ethene and propene. The highest barrier, both of ethene and propene formation, is found for the methylation of the side-chain towards the formation of an ethyl or isopropyl group. All other barriers are found to be substantially lower. This leads to a clear selectivity for ethene since the elimination of ethene with a rather low barrier competes with methylation towards propene which requires a barrier that is more than 100 kJ mol$^{-1}$ higher.

A mistake was found in the Matlab program used for the simulations. That is, a parameter of the Gibbs free energy change of zinc reduction (ΔG$^{0}$$_{Zn}$ $_{red.}$) was wrongly typed, which participates in eqn (31) and (37) of the original paper. ΔG$^{0}$$_{Zn}$ $_{red.}$ is calculated from the thermodynamic data of Goos et al.,1 and the equation with the correct data is as follows. ΔG$^{0}$$_{Zn}$ $_{red.}$= R·[8411.4 − 8.3237·T + 1.9335 × 10$^{-4}$·T$^{2}$ − 2.2728 × 10$^{-7}$·T$^{3}$−4.3047 × 10$^{-10}$·T$^{4}$ + 1.6777 × 10$^{-13}$·T$^{5}$ + 0.9824·T·ln(T)] (1) With the corrected parameter, the zinc solubility in copper (X$_{Zn}$) and, consequently, the zinc coverage (ϕ$_{Zn}$) have lower values than the originally published ones, as shown in the revised Fig. 4.

A three-site mean-field extended microkinetic model was developed based on ab initio DFT calculations from the literature, in order to simulate the conversion of syngas (H2/CO/CO2) to methanol on Cu (211) and Cu/Zn (211). The reaction network consists of 25 reversible reactions, including CO and CO2 hydrogenation to methanol and the water-gas shift reaction. Catalyst structural changes are also considered in the model. Experiments were performed in a plug flow reactor on Cu/ZnO/Al2O3 at various gas hourly space velocities (24–40 L h−1 gcat−1), temperatures (210–260 °C), pressures (40–60 bar), hydrogen feed concentrations (35–60% v/v), CO feed concentrations (3–30% v/v), and CO2 feed concentrations (0–20% v/v). These experiments, together with experimental data from the literature, were used for a broad validation of the model (a total of 690 points), which adequately reproduced the measurements. A degree of rate control analysis showed that the hydrogenation of formic acid is the major rate controlling step, and formate is the most sensitive surface species. The developed model contributes to the understanding of the reaction kinetics, and should be applicable for industrial processes (e.g. scale-up and optimization).

The manufacturing of technical catalysts generally involves a sequence of different process steps, of which co-precipitation is one of the most important. In this study, we investigate how continuous co-precipitation influences the properties of Cu/ZnO/ZrO2 (CZZ) catalysts and their application in the direct synthesis of dimethyl ether (DME) from CO2/CO/H2 feeds. We compare material characteristics investigated by means of XRF, XRD, N2 physisorption, H2-TPR, N2O-RFC, TEM and EDXS as well as the catalytic properties to those of CZZ catalysts prepared by a semi-batch co-precipitation method. Ultra-fast mixing in continuous co-precipitation results in high BET and copper surface areas as well as in improved metal dispersion. DME synthesis performed in combination with a ferrierite-type co-catalyst shows correspondingly improved productivity for CZZ catalysts prepared by the continuous co-precipitation method, using CO2-rich as well as CO-rich syngas feeds. Our continuous co-precipitation approach allows for improved material homogeneity due to faster and more homogeneous solid formation. The so-called &ldquo, chemical memory&rdquo, stamped during initial co-precipitation is kept through all process steps and is reflected in the final catalytic properties. Furthermore, our continuous co-precipitation approach may be easily scaled-up to industrial production rates by numbering-up. Hence, we believe that our approach represents a promising contribution to improve catalysts for direct DME synthesis

The direct synthesis of hydrogen peroxide over TiO$_{2}$-supported mono- and bimetallic Pd, PdSn, and PdIn nanoparticles (NPs) was performed in a continuous plug-flow reactor at 80 bar in ethanol with H$_{2}$ : O$_{2}$ ratios varied from 10 : 1 to 1 : 10. At the same time the catalysts were monitored by operando X-ray absorption spectroscopy (XAS). The setup optimized for XAS allowed productivities that are among the highest reported up to now. A rate of up to 580 mmol$_{H_{2}O_{2}}$ gcat$^{-1}$ h$^{-1}$ and a H$_{2}$O$_{2}$ concentration of 80 mmol l$^{-1}$ were obtained which were only limited by the supply of reactants. During H$_{2}$O$_{2}$ synthesis, the studied NPs revealed a face centered cubic (fcc) Pd(Sn/In) metal (alloy) structure at H$_{2}$ : O$_{2}$ ratios equal to or smaller than 1 and the corresponding β-hydride structure at H2 : O2 > 1. Under all conditions, additional SnO$_{2}$/In$_{2}$O$_{3}$ species were observed for the bimetallic catalysts. XAS supported by DFT calculations showed that alloying Pd with In or Sn limited the H$_{2}$ uptake capacity and the corresponding lattice expansion of the bimetallic NPs. Different catalysts performed best at different H$_{2}$ : O$_{2}$ ratios. All catalysts were stable at H$_{2}$ : O$_{2}$ > 1. Significant leaching of the active Pd and PdIn species could be observed for H$_{2}$ : O$_{2}$ ≤ 1 (quantified by XAS), while PdSn was relatively stable under these conditions. The higher stability of PdSn NPs is proposed to be due to a SnO$_{2}$ shell providing strong bonding between the NPs and the titania support.