Liquid-phase Catalytic Reactions Research Articles

Flexible SERS substrate In-situ monitoring of SPR-induced P-aminothiophenol dimerization

Surface-enhanced Raman spectroscopy (SERS) is an efficient technique for in-situ molecular investigation that is highly sensitive and has the ability to provide extensive fingerprint information. Additionally, the surface plasmons on the SERS substrate can also simultaneously induce the catalytic reaction. P-aminothiophenol (PATP) is a crucial model molecule utilized in SERS catalytic reactions. Through dimerization, PATP induced by the plasmon effect can produce 4,4’-dimercaptoazobenzene (DMAB). Here, a flexible SERS substrate with a monolayer of Au nanoparticles on polydimethylsiloxane (PDMS) is prepared and used for monitoring the dimerization of PATP. In the experiment, the SERS substrate is inverted, the side with Au nanoparticles monolayer is kept in contact with the PATP solution directly, and the laser is irradiated from the backside of the flexible substrate. The effects of Ag+ and oxygen concentrations on the reaction are investigated. This work paves the way for SERS methodology in in-situ monitoring of other liquid-phase catalytic reactions.

Nanosized Co-Fe spinel quantum dots anchored on activated carbon for enhanced VOCs mineralization via PMS-based AOPs coupled with wet scrubber

In this study, we have developed a liquid-phase wet washing process based on PMS advanced oxidation for the effective removal of toluene. Our approach involved synthesizing a high surface area composite catalyst (CFQ/AC) through a one-step process, in which 0 D CoFe2O4 was deposited onto low-cost activated carbon, endowing it with abundant surface-active sites that facilitate continuous PMS activation. The Co(Ⅲ)/Fe(Ⅲ) generated by the reaction captures electrons from the PMS, thus achieving Co(Ⅱ)/Fe(Ⅱ) regeneration and realizing two complete redox cycles of Co(Ⅲ)/Co(Ⅱ) and Fe(Ⅲ)/Fe(Ⅱ). During the liquid-phase catalytic reaction process, the CFQ/AC/PMS system consistently achieved a stable removal efficiency of over 96% within 2 h, with a selectivity of more than 80% for CO2, indicating high mineralization capability. Furthermore, based on the detection and analysis of GC–MS, there were few gaseous intermediates in the tail gas, leading to a significant reduction in secondary air pollution. By conducting electrochemical analysis and in-situ Raman spectroscopy, the transition metal valence changed and the combination of PMS with CFQ/AC formed charge transfer intermediates that led to toluene degradation. This mechanism utilized a cost-effective carbon-based composite catalyst, making it a practical and accessible solution for environmental applications.

Cover Feature: Near Infrared Light‐to‐Heat Conversion for Liquid‐Phase Oxidation Reactions by Antimony‐Doped Tin Oxide Nanocrystals (ChemPhysChem 7/2023)

The Cover Feature represents the action of antimony-doped tin oxide support for catalysts as an effective near infrared light-to-heat converter significantly enhancing the catalytic activity and selectivity for liquid-phase catalytic reactions due to the local heating of the catalyst surface with the bulk solution temperature maintained at ambient temperature. Cover design by Shin-ichi Naya. More information can be found in the Concept by Hiroaki Tada and co-workers.

Considerations when determining Counter-diffusion constants in liquid phase catalytic reactions using the Zero Length column (ZLC) method

The confusion with diffusion: In heterogeneous catalysis often, the catalytic material is housed within a porous support structure. It is important therefore to determine whether this support structure exerts limiting behaviors. In this paper, desorption and diffusion effects are separated under reactions conditions, to provide accurate effective diffusion constants in swelling and gate-opening catalysts. • A Zero Length Column (ZLC) method was developed using liquid chromatography. • Diffusion in porous catalyst pellets as small as 5 mg can be directly characterised. • Reactant counter-diffusion coefficients were determined for the Heck reaction. • Clear differences in diffusion rates for reactants versus non-reactant species. A Zero Length Column (ZLC) method was developed using a liquid chromatographic system to calculate reactant counter-diffusion coefficients in porous, solvent swollen catalytic pellets and gate-opening support materials. Reactant diffusivities within these porous materials were determined at the reaction conditions of 80 °C and 0.3–0.75 mL min −1 . For all materials, molecules of a similar size to the pore apertures, or molecules with strong interactions with the material surfaces, catalysts, were observable by the ZLC method, with both micro and macropore diffusion observed. Differences between Pd(II) and Pd(0) forms of the EnCat30 catalyst were examined to determine the effects of catalytic deactivation. The deactivated catalyst showed iodobenzene macroporous diffusion constants similar to the relatively inert toluene molecules. Finally, pulse field gradient NMR was utilised to compare and validate ZLC diffusion measurements for solvent swollen reaction systems. This study presents much needed novel findings on diffusivity data for liquid phase catalytic systems.

The new identity of cellulose pulp: A green silver nanoparticles support for highly efficient catalytic hydrogenation of 4-nitrophenol

The uniquely interconvertible transformation of cellulose pulp and paper shows great potential as smart materials for environment remediation. However, performing liquid-phase catalytic reactions involving hydrogenation steps under mild conditions and ambient temperature remains challenging. Herein, we report a facile and eco-friendly strategy to fabricate low-cost, highly effective, and stable pulp-supported silver nanoparticles (AgNPs/pulp). The pulp phase is used to maintain the high catalytic efficiency of the AgNPs/pulp catalyst, while the paper phase remains high stability as the filling material in the reaction column. The as-prepared AgNPs/pulp catalyst exhibits excellent catalytic activity toward NaBH4-mediated reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with a turnover frequency of 605.1 h−1 and a k value of 24.9 × 10−3 s−1 at room temperature, which outperforms most of reported cellulose-supported catalysts. Impressively, the AgNPs/pulp catalyst shows outstanding durability during a continuous operation for 72 h. Such excellent performance can be attributed to the uniform dispersion of the AgNPs/pulp in solution and uniform distribution of Ag NPs on the fiber surface of cotton pulp, which greatly improve the accessibility of reactants and active sites as well as metal-support interactions. This work provides new insights into the understanding of catalytic hydrogenation of 4-NP, which could pave the way for rational design of novel cellulose-based catalysts for organic wastewater treatment.

Co@C nanorods as both magnetic stirring nanobars and magnetic recyclable nanocatalysts for microcatalytic reactions

The rapid and effective mixing of reactants and catalysts is essential in liquid-phase catalytic reaction to boost mass transport. However, the routinely used magnetic stirring method is impractical for ultra-small systems such as lab-on-chip and flow cell due to the macroscale size of the magnetic bars. Herein, we developed a facile strategy to synthesize catalytically active magnetic Co@C nanorods, which could serve as both high-performance catalysts and magnetic stirring nanobars for micro-catalytic reactions. The Co@C core-shell structure endows the materials with high catalytic activity and excellent durability, while the strong magnetism of Co nanoparticles renders the nanorod catalyst unique stirring capability under an external rotating magnetic field, which significantly promotes the mass transport and also the catalytic efficiency in micro-catalytic reactions. Inspired by the unique structure and properties, the mixing ability and catalytic activity of Co@C nanorods were evaluated in several systems.

(Invited) 4-NP Reduction As a Reaction-Based Indicator for Quantitatively Assessing the Detrimental Influences of Leaching on Catalysts

The fundamental understanding of liquid-phase catalytic reactions is unavoidably complicated when the catalyst is prone to leaching since questions inevitably arise as to the true nature of the catalyst. While the catalytic reduction of 4-nitrophenol by borohydride is widely accepted as a trusted model reaction, it has faced little scrutiny concerning the potential impact of leached species or the appropriateness of assigning catalytic activity to the inserted nanostructures without rigorous experimental verification. Here, we present results from a spectroscopically monitored split test in which supported silver catalysts are physically separated from the reactants midway through the reaction. It is unambiguously demonstrated that the influence of leaching is far from benign, instead acting to extinguish the catalytic activity of the inserted nanostructures while giving rise to an unsupported species that is the true catalytic entity. With only sub-monolayer quantities of silver leached from the supported structures, the unsupported species must be exceedingly catalytic. Moreover, it is shown that leaching is inherent to aqueous media containing dissolved oxygen, without which the supported nanostructures remain catalytically active. With the same nanomaterial being able to act as either a heterogeneous catalyst or as a reservoir from which leached metal is derived, such influences have undoubtedly compromised prior studies. We, nevertheless, capitalize on the sensitivity of 4-nitrophenol reduction to leached species by using it as a reaction-based indicator able to quantitatively determine the time-dependence of the leaching process and enhancements to oxidative etching when silver, copper, palladium, platinum, and gold are exposed to chloride ions.

Process hazard evaluation for catalytic oxidation of 2-octanol with hydrogen peroxide using calorimetry techniques

In this work, various calorimetric and analytical techniques were implemented to identify reaction pathways and safety issues associated with the 2-octanol to 2-octanone two liquid phase catalytic reaction oxidative using aqueous hydrogen peroxide as oxidant, sodium tungstate (Na2WO4) as catalyst and methyltri-n-octylammonium hydrogen sulfate [CH3(n-C8H17)3N+HSO4−] as phase transfer catalyst. Differential scanning calorimetry (DSC) was employed to measure the temperature and heat flux of the reactant mixtures under dynamic scanning. Phi-TEC II adiabatic calorimeter was used to track temperature and pressure under worst runaway scenario. Isothermal reaction calorimeter (RC1e) was used to assess conditions relevant to normal process operations. Gas chromatography-mass spectrometry (GC–MS) was utilized to analyze final products of all measurements qualitatively and quantitatively. Data from both DSC and Phi-TEC II show that two highly exothermic reactions were detected with “onset” temperature at ~50 and ~220 °C, respectively. In all cases, only 2-octanol and 2-octanone were the identifiable compounds via GC–MS. 2-Octanol conversion was in the range of 15–50% and it reveals a linear correlation with overall heat generation. Data obtained verify that both exothermic peaks result from alcohol oxidation, thus indicating that in the conditions of the reaction and with the employed catalysts, hydrogen peroxide did not fully decompose at lower temperatures. Non-condensable gas generation measurements validated this argument. Based on those results, possible macroscopic reaction pathway was proposed. Furthermore, pressure and temperature profiles by PHI-TEC II indicated a potential transition to a homogeneous liquid phase at higher temperatures. The RC1e results verified that 2-octanol conversion was higher at higher stirring rates, while evaporative cooling of solvents tempered the reaction by removing the heat generated, thus improving safety. These findings can be further used to propose safer operating measures for design and scale-up of this reaction process to avert a potential runaway and to probe in the reaction pathways so as to increase inherently safer conditions for its performance.

Conceptual Design and Practical Challenges of Gas-Phase Catalytic Reactive Distillation/Absorption

Reactive distillation/absorption is among multifunctional reactors for process intensification. Conventionally, reactive distillation/absorption is suitable for liquid-phase catalytic reaction, with rare reports for gas-phase catalytic reaction. By reviewing the conventional reactive distillation/absorption concepts, we re-classify RD/A based on the criterion of phase state; and by analyzing the recent advances of column trays and catalyst development etc., we put forward novel conceptual design to conveniently achieve gas-phase catalytic reaction in reactive distillation/absorption process, which is termed as Gas-phase Catalytic Reactive Distillation/Absorption (GC-RD/A). The feasibility of this concept in theory and practice are analyzed from the perspective of catalyst, reactive internals and phase states. Practical challenges are presented comprehensively including equipment design, flow patterns, transport phenomena, reaction selection and operation window, and catalyst design, from fundamentals to industrial implementation.

Recent advances in metal-free carbon-based nanocatalysts

The catalytic reaction occupies an important position in the petroleum and chemical industry, and the traditional metal-based catalytic materials are hindered because of the limited reserves, poor stability, environmental pollution and so on. In recent years, with the promotion of green chemistry and sustainable chemical, metal-free carbon based nanomaterials and their applications in catalysts have attracted wide attention, and it has become a hot topic in the fields of energy, materials and chemical industry. In this paper, the relationship between the structure and catalysis of carbon-based nanomaterials is briefly introduced. When metal free carbon based materials directly used as catalysts, their catalytic active sites are mainly contain three types. Firstly, edge atoms and defect sites, whose carbon atoms are unsaturated and have high catalytic activity, can activate oxygen molecules and catalyze methane cracking. Secondly, functional groups on the surface of carbon materials. Different functional groups can catalyze different reaction systems. The oxygen-containing functional groups, for example, have certain weak acidity and they generally possess excellent catalytic performance in the acid-base reaction and multiple oxidation reactions. Thirdly, heteroatoms that replace carbon atoms into sp2 lattices will results in the changing of electron density distribution in carbon structure, which can promotion of chemical reactions by reducing the reaction energy barriers. The progress in the basic research on the application of metal-free carbon-based nanomaterials for the reaction of liquid phase, gas phase and photoelectricity in the last five years is reviewed. By in situ infrared characterization technique ( in situ FTIR) and density functional theory (DFT) calculations, the catalytic mechanism catalyzed by carbon materials was studied and the result indicates that most of the catalytic reactions are surface reactions, whose reaction rate are greatly affected by the specific surface area. The merit and demerit including, but not limited to catalytic efficient and stability of powder catalyst and monolith catalyst are list. Specially, our study shows that the construction of three-dimensional structured monolithic carbon-based catalytic materials can effectively avoid the separation problem of powder metal free carbon-based catalytic materials, and provides a reference for solving the practical bottleneck of metal free carbon-based catalytic materials in liquid phase catalytic reaction. In addition, based on the research basis of our group, the problems and future prospect of carbon-based nanomaterials are discussed from the aspect of the reaction engineering. Actually, there are few studies on the reaction engineering of metal free carbon based catalysts. At present, metal free carbon-based catalysts are mainly used in the form of ultra-fine powders. From the perspective of chemical magnification, carbon nanomaterials participate in catalytic reactions mostly in heterogeneous catalytic process, and their catalytic performance is obviously affected by catalyst dispersion, fluidity, mixed mass transfer and so on. Conventional reactors have some problems, such as weak mixing effect, blind zone of mixing, and poor inter-phase transfer effect, which lead to the contradiction between selectivity and reaction rate in the development of industrial catalytic technology of carbon nanomaterials. At the same time, there are still some problems in the traditional catalytic process, such as poor catalyst stability, easy agglomeration, and low recycling efficiency. Therefore, in order to realize the industrial scale application of metal free carbon nanomaterials catalytic reaction system, the research and development of industrial reactor suitable for the catalytic reaction process of carbon nanomaterials and its matching process is the key to form practical technology. Three-dimensional monolithic catalyst can effectively improve the efficiency of heat and mass transfer. It is expected to solve the problems of low efficiency of separation and process transfer of metal free carbon-based catalytic materials, simplify the process flow and avoid the loss of catalyst. Therefore, there is still a long way to go for the research and application of three-dimensional metal free carbon based catalysts in the future.

Identifying the True Catalyst in the Reduction of 4-Nitrophenol: A Case Study Showing the Effect of Leaching and Oxidative Etching Using Ag Catalysts

The fundamental understanding of liquid-phase catalytic reactions is unavoidably complicated when the catalyst is prone to leaching since questions inevitably arise as to the true nature of the catalyst. While the catalytic reduction of 4-nitrophenol by borohydride is widely accepted as a trusted model reaction, it has faced little scrutiny concerning the potential impact of leached species or the appropriateness of assigning catalytic activity to the inserted nanostructures without rigorous experimental verification. Here, we present results from a spectroscopically monitored split test in which supported silver catalysts are physically separated from the reactants midway through the reaction. It is unambiguously demonstrated that the influence of leaching is far from benign, instead acting to extinguish the catalytic activity of the inserted nanostructures while giving rise to an unsupported heterogeneous catalyst that is the true catalytic entity. With only submonolayer quantities of silver leached fro...

Encapsulating highly catalytically active metal nanoclusters inside porous organic cages

The creation of metal nanoclusters with dimensions ranging from subnanometre to ~2 nm for heterogeneous catalysis has received substantial attention. However, synthesizing these structures while retaining surface activity and avoiding aggregation is challenging. Here, we report a reverse double-solvents approach that enables encapsulation of highly catalytically active Pd nanoclusters inside the newly formed discrete organic molecular cage, RCC3. By encapsulating within the open cavities of soluble RCC3 cages, the obtained Pd nanocluster cores are produced with precisely controlled size (~0.72 nm) and show high solubility, excellent dispersibility and accessibility in solution, presenting significantly enhanced catalytic activities towards various liquid-phase catalytic reactions. Moreover, owing to the effective confinement of cage cavities, the as-prepared Pd nanoclusters possess excellent stability and durability. The strategy of encapsulation of metal nanoclusters within soluble porous organic cages is promising for developing stable and active catalysts.

Inhibitory effect of oxygenated heterocyclic compounds in mesoporous catalytic materials: A pulsed-field gradient NMR diffusion study

Oxygenated heterocyclic compounds are often used as solvents in liquid-phase catalytic reactions, such as hydrogenation and oxidation over porous oxide-based catalysts. It has often been reported that such compounds inhibit catalyst activity relative to the use of hydrocarbons as the solvent media. In this work we use 1H pulsed-field gradient (PFG) NMR diffusion studies to study diffusion properties of binary mixtures 1,4-dioxane/cyclohexane in mesoporous TiO2 over the whole composition range in order to understand the effect of the solid surface on molecular transport and molecular interactions within the pore space. The results reveal that whilst the diffusion of the hydrocarbon is only affected by geometrical restrictions, the diffusion profile of 1,4-dioxane is highly influenced by interactions within the catalyst pore, which is thought to be due to the presence of lone electron pairs on the oxygen atoms of 1,4-dioxane, allowing the molecule to act as a Lewis base when in contact with the solid surface. This agrees with findings on the inhibitory capacity of oxygenated heterocyclic compounds when used either as solvent in catalysis or present as impurities in some chemical feedstocks. The work shows that it is possible to use 1H PFG NMR in order to characterise the effect of surfaces on molecular transport and hence understand catalytic behaviour in liquid-phase catalytic reactions.

A microfiber catalyst with lemniscate structural elements

A new type of catalyst based on microfiber supports with microfibers twined into looped threads (lemniscate) that in turn form a structured flexible stable and geometrically regular bulk bed permeable to a reaction flow and not requiring any additional structurial elements is described. Deep toluene oxidation experiments show that the proposed platinum lemniscate glass-fiber catalyst (LGFC) considerably surpasses (by 8–10 times and more) familiar geometric types of catalysts, microfiber and otherwise, in both the specific observed activity per unit active component mass and the ratio between the observed activity and the specific hydraulic resistance. The reason for its superiority is a uniquely high efficiency of mass transfer in the external diffusion region of reactions. Among the promising fields of application for the proposed systems are fast gasphase catalytic reactions, liquid-phase catalytic reactions, and complicated reaction processes, in which the selectivity and the yield of target products are sensitive to diffusion inhibition.

ChemInform Abstract: Graphene‐Based Metal‐Free Catalysts for Catalytic Reactions in the Liquid Phase

AbstractReview: 95 refs.

Graphene-Based Metal-Free Catalysts for Catalytic Reactions in the Liquid Phase

The building blocks of the well-defined and easily modified carbon-bond structure of graphene sheet units bring unique characteristics to carbon materials. Especially when these carbon materials are nanosized, their tunable electronic states, giant conjugated structures, oxygen groups on the defects of graphene sheets, and various dopants all help make the materials active in liquid-phase catalytic reactions. In this mini-review, we mainly focus on the liquid-phase reactions catalyzed by carbon nanomaterials, and the related mechanisms are discussed on the basis of their structure fundamentals. In the final section, we also provide our perspectives on this rapidly developing carbocatalysis field.

ChemInform Abstract: Metal‐Organic Frameworks for Catalysis

AbstractReview: 91 refs.

Metal–Organic Frameworks for Catalysis

Metal–organic frameworks (MOFs) are a relatively new class of porous material, which are comprised of metal ions or clusters linked with poly-functional organic molecules. MOFs have been studied increasingly for heterogeneous catalysis applications because these hybrid materials have well-ordered tunable porous structures with exceptional textural properties and introduction of additional active sites can be carried out easily by relatively simple post-synthesis functionalization. This short review focuses on recent works on liquid phase catalytic reactions carried out over selected MOFs. The MOF membranes for catalysis and the potential of functionalized MOF materials for chiral reactions are also mentioned briefly.

Toward Homogenization of Heterogeneous Metal Nanoparticle Catalysts with Enhanced Catalytic Performance: Soluble Porous Organic Cage as a Stabilizer and Homogenizer.

Organic molecular cage (CC3-R) with intrinsically porous skeleton is used as a support for immobilizing Rh nanoparticles (NPs) in an ultrasmall size of ∼1.1 nm for the first time. The CC3-R with the unique characteristic of high solubility can be utilized to homogenize the heterogeneous catalyst in solution. The obtained homogenized heterogeneous catalyst Rh/CC3-R-homo exhibits significantly enhanced catalytic performance toward various liquid-phase catalytic reactions, as compared with the heterogeneous counterpart Rh/CC3-R-hetero. Moreover, Rh/CC3-R-homo shows excellent durability and recyclability. The advantage of combining homogeneous and heterogeneous catalysts is likely to be beneficial for many applications.

ChemInform Abstract: Mesoporous Materials: Versatile Supports in Heterogeneous Catalysis for Liquid Phase Catalytic Transformations

AbstractReview: 158 refs.