Catalytic conversion of biomass to biophenol

The invention relates to a demethoxylation process for demethoxylating alkylmethoxyphenols using an aromatic solvent to produce alkylphenols. The invention also relates to dealkylation process for dealkylating alkylphenols using an aromatic solvent to produce phenol. The invention further relates to a tandem demethoxylation and dealkylation process, which can be performed in a single reactor. The process is useful in the conversion of lignin derived alkylmethoxyphenols into biophenol

Identifying the Role of Brønsted and Lewis Acid Sites in the Diels-Alder Cycloaddition of 2,5-DMF and Ethylene

The role of Lewis and Brønsted acid sites in the Diels-Alder cycloaddition (DAC) of ethylene to 2,5-dimethylfuran (2,5-DMF) to p-xylene was investigated. Amorphous silica catalysts containing Al3+ (ASA), Ga3+ (ASG), and In3+ (ASI) were prepared via homogeneous deposition-precipitation. Silica modified with Zr4+ (ASZ) was prepared by impregnation. Their acidic properties were characterized by various IR and NMR spectroscopic techniques. Measurements using pyridine as a probe molecule highlighted the presence of mostly Lewis acid sites (LAS) in all materials. Using CO as a probe, in contrast, demonstrated the existence of Brønsted acid sites (BAS) in ASA and ASG, which were nearly absent in ASI and ASZ. Differences in basic strength can explain the contrast in results observed between the two probe molecules. The highest p-xylene yield (~20%) in the DAC reaction, could be achieved with ASA and ASG. The lack of BAS in ASI and ASZ resulted in inferior performance in the DAC, with p-xylene yields below 5%. These results indicate the importance of BAS for the DAC reaction. Several other heterogeneous and homogeneous catalysts were explored for the DAC reaction to show the generality of our conclusion that BAS play a critical role in obtaining p-xylene from 2,5-DMF and ethylene

Computational study of CO2 methanation on Ru/CeO2 model surfaces:On the impact of Ru doping in CeO2

The Sabatier reaction (CO 2 + H 2 → CH 4 + H 2O) can contribute to renewable energy storage by converting green H 2 with waste CO 2 into CH 4. Highly dispersed Ru on CeO 2 represents an active catalyst for the CO 2 methanation. Here, we investigated the support effect by considering a single atom of Ru and a small Ru cluster on CeO 2 (Ru 6/CeO 2). The influence of doping CeO 2 with Ru was investigated as well (Ru 6/RuCe x-1O 2x-1). Density functional theory was used to compute the reaction energy diagrams. A single Ru atom on CeO 2 can only break one of the C-O bonds in adsorbed CO 2, making it only active in the reverse water-gas shift reaction. In contrast, Ru 6 clusters on stoichiometric and Ru-doped CeO 2 are active methanation catalysts. CO is the main reaction intermediate formed via a COOH surface intermediate. Compared to an extended Ru(11-21) surface containing step-edge sites where direct C-O bond dissociation is facile, C-O dissociation proceeds via H-assisted pathways (CO → HCO → CH) on Ru 6/CeO 2 and Ru 6/RuCe x-1O 2x-1. A higher CO 2 methanation rate is predicted for Ru 6/RuCe x-1O 2x-1. Electronic structure analysis clarifies that the lower activation energy for HCO dissociation on Ru 6/RuCe x-1O 2x-1 is caused by stronger electron-electron repulsion due to its closer proximity to Ru. Strong H 2 adsorption on small Ru clusters explains the higher CO 2 methanation activity of Ru clusters on CeO 2 compared to a Ru step-edge surface, representative of Ru nanoparticles, where the H coverage is low due to stronger competition with adsorbed CO.</p

Unravelling CO Activation on Flat and Stepped Co Surfaces: A Molecular Orbital Analysis

Structure sensitivity in heterogeneous catalysis dictates the overall activity and selectivity of a catalyst whose origins lie in the atomic configurations of the active sites. We explored the influence of the active site geometry on the dissociation activity of CO by investigating the electronic structure of CO adsorbed on 12 different Co sites and correlating its electronic structure features to the corresponding C-O dissociation barrier. By including the electronic structure analyses of CO adsorbed on step-edge sites, we expand upon the current models that primarily pertain to flat sites. The most important descriptors for activation of the C-O bond are the decrease in electron density in CO’s 1π orbital , the occupation of 2π anti-bonding orbitals and the redistribution of electrons in the 3σ orbital. The enhanced weakening of the C-O bond that occurs when CO adsorbs on sites with a step-edge motif as compared to flat sites is caused by a distancing of the 1π orbital with respect to Co. This distancing reduces the electron-electron repulsion with the Co d-band. These results deepen our understanding of the electronic phenomena that enable the breaking of a molecular bond on a metal surface.</p

Electrochemical interfaces during CO₂ reduction on copper electrodes

Copper has received significant attention for decades as electrode material for the electrochemical reduction of carbon dioxide (CO2RR) because of its capability to form multi-carbon products (C2+). However, despite substantial research, CO2RR with Cu-based electrocatalysts has yet to be commercialized. Understanding the physical and chemical changes of the catalyst surface and the dynamics of the electrochemical interface during CO2RR is key to improve the activity and selectivity. This review article focuses on recent studies that provide important insights of the surfaces and interfaces during reduction using ex-situ, in-situ and operando characterization techniques.</p

Al Promotion of In2O3 for CO2 Hydrogenation to Methanol

In2O3 is a promising catalyst for the hydrogenation of CO2 to methanol, relevant to renewable energy storage in chemicals. Herein, we investigated the promoting role of Al on In2O3 using flame spray pyrolysis to prepare a series of In2O3−Al2O3 samples in a single step (0−20 mol % Al). Al promoted the methanol yield, with an optimum being observed at an Al content of 5 mol %. Extensive characterization showed that Al can dope into the In2O3 lattice (maximum ∼ 1.2 mol %), leading to the formation of more oxygen vacancies involved in CO2 adsorption and methanol formation. The rest of Al is present as small Al2O3 domains at the In2O3 surface, blocking the active sites for CO2 hydrogenation and contributing to higher CO selectivity. At higher Al content (≥10 mol %Al), the particle size of In2O3 decreases due to the stabilizing effect ofAl2O3. Nevertheless, these smaller particles are prone to sintering duringCO2 hydrogenation since they appear to be more easily reduced. These findings show subtle effects of a structural promoter such asAl on the reducibility and texture of In2O3 as a CO2 hydrogenation catalyst

Ni and ZrO₂ promotion of In₂O₃ for CO₂ hydrogenation to methanol

Transition metals, such as Ni, Pd, and Pt, and ZrO2 are known as efficient promoters in M-In2O3-ZrO2 catalysts for CO2 hydrogenation to methanol. Herein, we systematically investigated the role of Ni and ZrO2 promoters by preparing ternary NiO-In2O3-ZrO2 catalysts and binary counterparts by flame spray pyrolysis. The highest methanol rate was obtained for the Ni(6 wt%)-In2O3(31 wt%)-ZrO2(63 wt%) composition. DRIFTS-SSITKA shows that formate is the key intermediate in the hydrogenation of CO2 to methanol. Kinetic analysis shows the competition between methanol and CO formation. The rate-limiting step in methanol formation is likely the hydrogenation of surface methoxy species. Ni and ZrO2 play different promoting roles without showing synergy with respect to each other. Ni promotes hydrogenation of surface formate and methoxy species, while ZrO2 maintains a high In2O3 dispersion, the smaller In2O3 size likely stabilizing formate and other intermediates during their conversion to methanol.</p

Ammonia electrocatalytic synthesis from nitrate

The interest in electrochemical processes to produce ammonia has increased in recent years. The motivation for this increase is the attempt to reduce the carbon emissions associated with its production, since ammonia is responsible for 1.8% of the global CO2 emissions. Moreover, green ammonia is also seen as a possible transportation fuel in various renewable energy transition scenarios. Several electrochemical processes are being investigated such as N2, NO3–, or NO conversion. Since nitrates are an attractive source of nitrogen, due to their role as water contaminants and facility to break N-O bonds, this mini review is focused on the electrocatalytic synthesis of ammonia from NO3− reduction. Here, we summarized the important work on reaction mechanisms and electrocatalysts for this reaction.</p

Coverage effects in CO dissociation on metallic cobalt nanoparticles

The active site of CO dissociation on a cobalt nanoparticle, relevant to the Fischer-Tropsch reaction, can be computed directly using density functional theory. We investigate how the activation barrier for direct CO dissociation depends on CO coverage for step-edge and terrace cobalt sites. Whereas on terrace sites increasing coverage results in a substantial increase of the direct CO dissociation barrier, we find that this barrier is nearly independent of CO coverage for the step-edge sites on corrugated surfaces. A detailed electronic analysis shows that this difference is due to the flexibility of the adsorbed layer, minimizing Pauli repulsion during the carbon-oxygen bond dissociation reaction on the step-edge site. We constructed a simple first-principles microkinetic model that not only reproduces experimentally observed rates but also shows how migration of carbon species between step-edge and terrace sites contributes to methane formation

Titanium Phosphate Grafted on Mesoporous SBA-15 Silica as a Solid Acid Catalyst for the Synthesis of 5-Hydroxymethylfurfural from Glucose

The grafting of titania on SBA-15 followed by its phosphation was presented to prepare a mesoporous Lewis–Brønsted bifunctional solid acid catalyst for the tandem conversion of glucose via fructose to 5-hydroxymethylfurfural (HMF). Titania was dispersed on SBA-15 as an amorphous surface layer containing abundant coordinatively unsaturated tetrahedral Ti ions, which was reactive and readily transformed upon phosphation into a new titanium phosphate phase with the chemical formula identified as Ti2O3(H2PO4)2·2H2O. The ordered mesoporous structure was well maintained after three modification cycles, affording a desirable surface area of over 300 m2/g. The SBA-15-supported titanium phosphate layer affords higher overall acidity and Brønsted to Lewis acid ratio, compared with the conventional post-phosphated bulk anatase titania. The tetrahedral Ti ions and the adjacent protonated phosphate groups on the titanium phosphate layer could form Lewis–Brønsted acid pairs at molecular level proximity, which largely enhanced the selective tandem catalysis for glucose conversion via fructose to HMF. An optimized HMF yield of 71% was achieved at 160 °C in a water–methyltetrahydrofuran biphasic system over the SBA-15-supported titanium phosphate catalyst. The catalyst exhibited good hydrothermal stability with a rather limited silicon and phosphate leaching, and no distinct pore collapse or performance loss over three sequential reaction runs