Increase In Reaction Rate Research Articles

Anl-proline-modified chiral porous hyper-crosslinkedl-phenylalanine dipeptide—increased reaction rate and selectivity in asymmetric catalysis

Two heterogeneous catalysts were synthesized from aromatic amino acids. Asymmetric Michael addition reaction and Mannich reaction were catalyzed, and the product shows a high ee value.

Selective photodimerization of acenaphthylene in polymersome nanoreactors.

PEG-b-PLA polymersomes are used as nanoreactors for the photodimerization of acenaphthylene (ACE), increasing reaction rate significantly. The reaction steered towards almost exclusive formation of anti product (94 : 6). This selectivity is remarkable, as other known systems commonly mediate formation of the syn product.

Chemically reacting mixing in coaxial miscible liquid jets under variable viscosities and reaction rates

We study the mixing and reactions between two fluids with disparate viscosities in a co-axial flow at high Schmidt number, through numerical simulations. The chemical reactions chosen in this work are competitive-consecutive in nature. Numerical implementation of the reactions proceeds as given by Li and Toor (1986), in a Large-Eddy Simulation (LES) framework. The aim of the present study is to investigate the effect of reaction rate constant ratio on the product and byproduct formations under distinct viscosity ratios between the annular and central jets. Flow features promoting mixing and reactions such as turbulence, engulfment, jet instability, waves and break-up are described. The effect of viscosity difference between the jet and co-flow on the mixing and reactions are also delineated. It is found that selectivities of the undesirable product decrease with reducing viscosity ratio as well as increasing reaction rate constant ratio.

Excitation function for theLi6+αreaction between 0.5 and 1.4 MeV

The recent discovery of carbon enhanced metal poor (CEMP) stars leaves open questions as to how carbon, nitrogen, and oxygen (CNO) elements were enriched through the nucleosynthesis of primordial elements in the first stars. It has been proposed that the reaction sequence $^{6}\mathrm{Li}(\ensuremath{\alpha},\ensuremath{\gamma})^{10}\mathrm{B}(\ensuremath{\alpha},d)^{12}\mathrm{C}$ may offer an alternative path to the traditional triple-$\ensuremath{\alpha}$ process, taking advantage of $\ensuremath{\alpha}$ cluster configurations in the $^{10}\mathrm{B}$ and $^{14}\mathrm{N}$ compound nuclei. In the present study, an investigation of the low-energy $^{6}\mathrm{Li}(\ensuremath{\alpha},\ensuremath{\gamma})^{10}\mathrm{B}$ cross section is performed using a combination of different $\ensuremath{\gamma}$ ray detectors. The discrepancies in the literature of the width of the broad resonance (${E}_{\text{c.m.}}=1200$ keV, ${1}_{3}^{+}$) are resolved. A consistent and much more precise width, ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\alpha}}=125(8)$ keV, is obtained via a simultaneous $R$-matrix fit of the data from the present study and that reported previously in the literature. The uncertainty in the tail contribution of the broad resonance indicates that a substantial increase in the low temperature reaction rate is possible compared to that adopted by the REACLIB compilation.

Nano-sized Metallic Nickel Clusters Stabilized on Dealuminated beta-Zeolite: A Highly Active and Stable Ethylene Hydrogenation Catalyst

Supported Ni catalysts were synthesized using the beta-zeolite framework, with and without the framework Al, as a platform for dispersing Ni. The silanol nest sites of dealuminated zeolite beta provide isolated cationic Ni sites that can be reduced under relatively mild conditions to create highly dispersed metal clusters. Compared to the Ni sites present in Ni-[Al]-beta-19, Ni-[DeAl]-beta exhibit a 20-fold increase in the apparent reaction rate for C2H4 hydrogenation and is stable, with little deactivation over 16 h of catalysis. Ni K-edge X-ray absorption spectroscopy (XAS), as well as CO adsorption monitored with Fourier transform infrared spectroscopy, shows that in the oxidized Ni-[DeAl]-beta catalyst Ni reoccupies vacant silanol nests produced from dealumination. After reductive treatment, XAS shows that approximately 50% of Ni is reduced to metallic Ni, forming clusters that are approximately 1 nm in size. Scanning transmission electron microscopy images are consistent with the absence of large (>1 nm) metallic Ni clusters. These results indicate that [DeAl]-beta can be used to synthesize isolated cationic Ni sites as well as stabilize highly dispersed metal clusters that can be used as a highly active and stable C2H4 hydrogenation catalyst.

DFT–kMC Analysis for Identifying Novel Bimetallic Electrocatalysts for Enhanced NRR Performance by Suppressing HER at Ambient Conditions Via Active-Site Separation

As an alternative to the traditional Haber-Bosch process for ammonia synthesis under high temperature and pressure, the electrochemical nitrogen reduction reaction (NRR) under ambient conditions has been getting attention. Although ruthenium (Ru) is considered the holy-grail catalyst for the NH3 process, it suffers from low selectivity due to the competition between NRR and hydrogen evolution reaction. Experimental screening of new candidate catalysts that can circumvent this challenge is highly resource-intensive, requiring significant labor and expensive precursors. To address this challenge, we have combined density functional theory and kinetic Monte Carlo to shortlist high-performing NRR catalysts. Specifically, this framework utilizes a combination of thermodynamic, electronic, and kinetic analyses to investigate different bimetallic catalysts (i.e., RuTi, RuV2, Ru3W, RuZn3, and RuZr) with specially designed separate active sites for N2 and H adsorption to enhance NRR performance. Our investigations revealed that the newly suggested RuV2 has superior NRR activity with decreased thermodynamic overpotential and increased reaction rates that surpass those of Ru. Notably, RuV2 shows a high N2 selectivity by significantly reducing H poisoning on the catalyst surface and increasing the amount of NH3 with a turnover frequency of 1.1 × 10–4 s–1 under mild conditions (300 K and 1 bar), which is 1 000 times greater than that of a pure Ru electrocatalyst. Given these key observations, we believe our framework can play a pivotal role in elucidating the role of different active sites for NRR and can be extended to other high-impact metallic catalyst families in the future.

Mathematical analysis to the variation of tumor cells density according to recovery of five organs: Kidney, liver, heart, spleen, and lung

Background and objectiveHarmonious interactions of five representative organs: kidney, liver, heart, spleen, and lung, improve metastasis and cell divisions, and abnormal cell division causes cancer cell development. The research is processed through a mathematical approach based on win-win principle of five organs to generate medicine in blood vessel. The variations of solute medicine amount in blood vessel with respect to the flow rates of injected drugs are interpreted. The alterations of tumor cells density and tumor angiogenesis factor concentration are described according to the recovery of five organs’ functions. MethodsA compartmental analysis is applied to obtain medicine concentration in blood vessel by the functional recovery of five organs considering time level ti, the reaction rate coefficient Rj, and the medicine flow rate α. Random motility and chemotaxis in response to tumor angiogenesis factor gradients are comprised to derive mathematical governing equations for tumor cells motion and a finite volume method with time-changing is adopted to obtain numerical solutions due to the complexity of the governing equations. ResultsDrug concentration in blood vessel grows as heart reaction rate increases, and the medicine made through the functional enhancements of five representative organs is highly influential to restrain the activity of tumor angiogenesis factor. With the growth of medicine concentration in blood vessel according to the decline of reaction rate and medicine flow rate, tumor cells reacts hypersensitively at the moment of medicines injection and the density of tumor cells approached to zero. ConclusionsConsequently, reaction rate, time level, and medicine flow rate are crucial factors in the determination of medicine amount in blood vessel and to control tumor angiogenesis factor concentration, and harmonious balanced functions among five organs based on win-win principle contribute to control the activity of tumor cells.

Multi-Resonant Thermally Activated Delayed Fluorescent (MR-TADF) Compounds as Photocatalysts.

Donor-acceptor (D-A) thermally activated delayed fluorescent (TADF) compounds, such as 4CzIPN, have become a widely used sub-class of organic photocatalysts for a plethora of photocatalytic reactions. Multi-resonant TADF (MR-TADF) compounds, a subclass of TADF emitters that are rigid nanographene derivatives, such as DiKTa and Mes3 DiKTa, have to date not been explored as photocatalysts. In this study both DiKTa and Mes3 DiKTa were found to give comparable or better product yield than 4CzIPN in a range of photocatalytic processes that rely upon reductive quenching, oxidative quenching, energy transfer and dual photocatalytic processes. In a model oxidative quench process, DiKTa and Mes3 DiKTa gave increased reaction rates in comparison to 4CzIPN, with DiKTa being of particular interest due to the lower material cost (£0.94/mmol) compared to that of 4CzIPN (£3.26/mmol). These results suggest that DiKTa and Mes3 DiKTa would be excellent additions to any chemist's collection of photocatalysts.

YSZ-based mixed potential type acetone gas sensor attached with CuSb2O6 sensing electrode for ketosis diagnosis

Acetone in exhaled breath can be employed as a diabetic-specific biomarker for noninvasive, painless, quick and in-house screening of diabetes. Herein, a mixed potential type acetone gas sensor using yttria-stabilized zirconia (YSZ) and CuSb 2 O 6 sensing electrode (SE) was manufactured. The sensitivities of the sensor to 0.2–5 ppm acetone and 5–200 ppm acetone were − 24.9 mV/decade and − 76.2 mV/decade at 680 °C. The response time for 10 ppm acetone of the sensor was only 3 s and the recovery time was 17 s. The sensor also displayed good repeatability, long-term stability, reliability and selectivity. It was worth noting that the response value of the sensor increased with the increase of relative humidity (RH) value, which could be account for the increase of acetone gas concentration and electrochemical reaction rate at TPB. Moreover, the sensor could realize the distinction between the diabetic ketosis patients and non-ketotic volunteers by the response values of the sensor in the clinical breath detection, proving its potential in the field of ketosis diagnosis. • CuSb 2 O 6 material is used as sensing electrode to fabricate a mixed potential type YSZ-based acetone sensor. • The sensor with CuSb 2 O 6 -SE exhibits high sensitivity, response and recovery speed and selectivity to acetone at 680 °C. • The acetone gas concentration and electrochemical reaction rate at TPB increased with the increase of RH. • The sensor could also realize the distinction between the diabetic ketosis patients and non-ketotic volunteers.

Advances in Matrix-Supported Palladium Nanocatalysts for Water Treatment.

Advanced catalysts are crucial for a wide range of chemical, pharmaceutical, energy, and environmental applications. They can reduce energy barriers and increase reaction rates for desirable transformations, making many critical large-scale processes feasible, eco-friendly, energy-efficient, and affordable. Advances in nanotechnology have ushered in a new era for heterogeneous catalysis. Nanoscale catalytic materials are known to surpass their conventional macro-sized counterparts in performance and precision, owing it to their ultra-high surface activities and unique size-dependent quantum properties. In water treatment, nanocatalysts can offer significant promise for novel and ecofriendly pollutant degradation technologies that can be tailored for customer-specific needs. In particular, nano-palladium catalysts have shown promise in degrading larger molecules, making them attractive for mitigating emerging contaminants. However, the applicability of nanomaterials, including nanocatalysts, in practical deployable and ecofriendly devices, is severely limited due to their easy proliferation into the service environment, which raises concerns of toxicity, material retrieval, reusability, and related cost and safety issues. To overcome this limitation, matrix-supported hybrid nanostructures, where nanocatalysts are integrated with other solids for stability and durability, can be employed. The interaction between the support and nanocatalysts becomes important in these materials and needs to be well investigated to better understand their physical, chemical, and catalytic behavior. This review paper presents an overview of recent studies on matrix-supported Pd-nanocatalysts and highlights some of the novel emerging concepts. The focus is on suitable approaches to integrate nanocatalysts in water treatment applications to mitigate emerging contaminants including halogenated molecules. The state-of-the-art supports for palladium nanocatalysts that can be deployed in water treatment systems are reviewed. In addition, research opportunities are emphasized to design robust, reusable, and ecofriendly nanocatalyst architecture.

Solar-driven semi-conductor photocatalytic water treatment (TiO2, g-C3N4, and TiO2+g-C3N4) of cyanotoxins: Proof-of-concept study with microcystin-LR

Cyanobacteria and their toxins are a threat to drinking water safety as increasingly cyanobacterial blooms (mass occurrences) occur in lakes and reservoirs all over the world. Photocatalytic removal of cyanotoxins by solar light active catalysts is a promising way to purify water at relatively low cost compared to modifying existing infrastructure. We have established a facile and low-cost method to obtain TiO2 and g-C3N4 coated floating photocatalysts using recycled glass beads. g-C3N4 coated and TiO2+g-C3N4 co-coated beads were able to completely remove microcystin-LR in artificial fresh water under both natural and simulated solar light irradiation without agitation in less than 2 h. TiO2 coated beads achieved complete removal within 8 h of irradiation. TiO2+g-C3N4 beads were more effective than g-C3N4 beads as demonstrated by the increase reaction rate with reaction constants, 0.0485 min−1 compared to 0.0264 min−1 respectively, with TiO2 alone found to be considerably slower 0.0072 min−1. g-C3N4 based photocatalysts showed a similar degradation pathway to TiO2 based photocatalysts by attacking the C6–C7 double bond on the Adda side chain.

Electrochemical Catalysis Generated By an External Electric Field in Conjunction with a Low Density-of-States Conductor

In electrochemistry the reaction rate depends strongly on the voltage difference applied between the two electrodes. A voltage increase at the electrodes will generate a larger electric field in the electric double layer (EDL), which increases the reaction rate, but this will also cause additional power to be dissipated. We show both theoretically and experimentally that one can increase the electrochemical reaction rate, at no additional cost in power, by utilizing an external electric field in the proximity of a material catalyst. This is not surprising since, although the exact mechanism for catalysis due to a material compound can be quite intricate, the basic underlying physical processes for catalysis can often be shown to be due to the molecular electric field at a specific catalyst surface site. Here we generalize this observation and show how the application of a ‘simple external’ electrostatic field in conjunction with a low density-of-states conductor such as graphene can be used to intensify the already large electric field in the EDL layer - thus accelerating the reaction rate without additional power dissipation. We focus on water electrolysis (more specifically, the hydrogen evolution reaction - HER) in our electrochemical reaction study. Based on our observed experimental results as well as our theoretical analysis we show how an electrode incorporating trapped charge at the interface between two dielectrics will generate a large electrostatic field which, in conjunction with the quantum capacitance of a low density-of-states conductor, allows penetration of this field into the electric double layer (EDL), thereby adding to the original EDL field and thus, functioning as a reaction rate accelerant or a catalyst. Our experiment shows a 100% increase in the hydrogen generation rate for the HER reaction when employing our external electrostatic ‘catalyst’ technique. Since this method depends primarily on the enhancement of the EDL electric field for the reaction rate increase, it can be universally applied to all electrochemical reactions without requiring a detailed molecular level understanding of the reaction of interest.

Clean iron removal from zinc leaching solution by shear enhancement: Industrial pilot campaign and strengthening mechanism

A clean goethite process for iron removal was proposed to overcome the challenges of large amount of hazardous iron waste and low reaction rate. First, the forms of substances in zinc leaching solution and iron precipitation residue were analyzed by thermodynamic calculation. The process parameters were then optimized by industrial test, and the strengthening mechanism was revealed by numerical simulation. Finally, the industrial application of the process was evaluated. Results indicated that the stable phase of goethite existed in the pH range of 2.8–4.2 at 80 °C. The concentration of iron was reduced from 11.94 g L−1 to 2.08 g L−1 at 6 h under optimal conditions, and the iron and zinc contents in the residue with needle structure were 49.95 wt% and 6.02 wt%, respectively. The shear-enhanced process accelerated the flow rate and improved the gas dispersion, leading to the rapid homogenization of solution and increased reaction rate. In addition, the oxygen utilization rate of the shear-enhanced goethite process was 39.33% higher than that of the traditional process. The shear-enhanced process achieved a 20% reduction in waste residue, and the production cost was 0.85 $ kg−1.

Nanoparticle Shapes Effects on MHD Flow of Hybrid Nanofluid over a Stretching/Shrinking Sheet with Slip and Chemical Reaction

The impact of nanoparticle shapes (i.e., blade, brick, cylindrical, platelet, and spherical) on the MHD flow of Ag-MgO/water hybrid nanofluid over a stretching/shrinking sheet is scrutinized in this study. Chemical reaction and activation energy are included in the governing partial differential equations of the flow problem. On the boundary, velocity slip and zero mass flux conditions are considered. The simplification of the governing equations and boundary conditions into non-linear ordinary differential equations is done through similarity transformation. Then, the bvp4c solver in Matlab is deployed for computation, with the results generated in the form of numerical solutions and graphs. It is found that the usage of spherical-shaped nanoparticles produces the lowest magnitude of skin friction coefficient, and the implementation of blade-shaped nanoparticles in the hybrid nanofluid provides the highest enhancement of heat transfer rate. The increment in activation energy slows down the chemical reaction that raises the concentration profile of the hybrid nanofluid. However, the concentration profile decreases as the reaction rate increases.

Facile and scalable synthesis of Fe-based metal organic frameworks for highly efficient photo-Fenton degradation of organic contaminants

Fe-based metal organic frameworks (Fe-MOFs) being a newly developed photo-Fenton catalyst, have gained ever-increasing attention for environmental remediation, but have been limited by high synthesis cost (high energy-consumption and low yield). In this work, economical and scalable synthesis of Fe-BDC1 (BDC denotes as terephthalic acid) was achieved via facile stirring under ambient condition, and its adsorptive, photocatalytic, Fenton-like and photo-Fenton performances were comprehensively explored against contaminants removal. In comparison, synthesized Fe-BDC2 with the common solvothermal method, the yield of Fe-BDC1 increased 3.4 times. Also, its adsorption capacity towards Rhodamine B (Rh. B) increased about 5.85 times. Moreover, the significantly improved degradation of Rh. B was observed in the Fenton-like and photo-Fenton systems with the increased reaction rate constants up to 4.90 and 2.33 times, respectively. This enhanced catalytic performance of Fe-BDC1 was mainly attributed to the enlarged specific surface area (SSA) and favorable electron separation and migration, resulting into the accelerated ≡Fe(II)/≡Fe(III) cycle and increased yield of reactive oxidative species (ROSs). Additionally, the unique light-induced adsorption enhancement further strengthened the contaminants removal. Fe-BDC1 as photo-Fenton catalyst was found superior over conventional catalysts in terms of advantages including: low dose requirement of catalysts (decrease in an order of magnitude) and H2O2, wide pH working range (3.0–9.0), excellent reusability and stability, universal removal behavior against all organic pollutants, and remarkable synergism between photocatalysis and Fenton-like process with synergistic factor of 77.23%. Moreover, the Fe coordinative unsaturated sites (Fe CUSs) and ·OH were determined as the active sites and the main ROSs, respectively, responsible for highly efficient pollutant degradation. This work gives a feasible solution for the preparation of Fe-MOFs with low synthesis cost and high yield, paving ways for their practical mass application in heterogeneous photo-Fenton oxidation.

Combustion of N-Decane+air Mixtures To Investigate Laminar Burning Velocity Measurements At Elevated Temperatures

ABSTRACT The combustion characteristics of n-decane+air mixtures are experimentally investigated through laminar burning velocity measurements at 1 atm pressure and higher initial temperatures using an externally heated diverging channel (EHDC) method. Up to 610 K mixture temperature over an equivalence ratio range of 0.7–1.4, laminar burning velocities are reported with an accuracy of ± 5%. The current measurements exhibit a good match with existing experimental measurements, and agree closely with the predictions of Zhao, LLNL and PoliMi mechanisms at different mixture temperatures. The present measurements show an excellent match of temperature exponent (α) variation with equivalence ratio (ϕ) with the predictions of distinct kinetic models as well as experimental measurements. This study reveals that a substantial scatter exists among the predictions of different kinetic models. A variation of 20–30 cm/s in the burning velocity is observed at 610 K mixture temperature. Reaction R16 (H + HO2 = H2 + O2), which inherently reduces the burning velocity becomes insignificant at an elevated mixture temperature of 610 K, and the reaction R15 (H + HO2 = 2OH) plays a dominant role in accelerating the flame propagation. From reaction pathway diagrams, it is clear that a higher burning velocity at 610 K is associated with the increased reaction rate. The elemental-flux value associated with the formation of C2H3 from C2H4 at 610 K mixture temperature is ≅34% higher in comparison to the 470 K mixture temperature.

Process hazard evaluation and thermal runaway prediction for styrene polymerization initiated by peroxide-azo composites

Styrene is an important monomer for synthetic resins, ion exchange resins and synthetic rubber. Styrene polymerization requires the use of initiators to increase the reaction rate, with composite initiators showing promise for increased reaction rates. However, increased reaction rates in polymerization, if uncontrolled, can lead to thermal runaway with disastrous consequences. Numerous runaway incidents have been documented, indicating inadequate awareness of the thermal hazards of polymerization reactions. This study focuses on determining via calorimetric techniques the thermal hazards of styrene polymerization using azodiisobutyronitrile (AIBN) and tert-Butyl peroxybenzoate (TBPB) composite initiators. Differential scanning calorimetry (DSC) is employed to investigate the thermal decomposition properties of composite initiators with varying composition. Non-isothermal experiments and adiabatic experiments are used to determine the thermal hazard parameters including initial exothermic temperature and heat release of styrene polymerization. The risk of secondary reactions is evaluated by reaction calorimetry (RC1e) and product thermogravimetric analysis (TGA). Key safety parameters of the exothermic reaction, such as the onset temperature, heat release, time to maximum rate under adiabatic condition as well as activation energy, are presented. The results show that the thermal hazard of the polymerization reaction is lowest when the ratio of AIBN to TPPB in the composite initiator is 1:1. In this scenario, the temperature reached by the uncontrolled reaction does not provoke the decomposition of the products, yet the runaway consequences are still unacceptable. This work provides extensive data as a reference for the process optimization of styrene polymerization from the perspective of safety.

Entropy reduction from strong localization – an explanation for enhanced reaction rates of organic synthesis in aqueous micelles

HypothesisThe underlying mechanism for increased reaction rates in micellar catalysis-based organic synthesis is a reduced entropy barrier for the reaction. A two-dimensional localization of reactants and catalyst in the surfactant micelle reduces the translational entropy of all components. The entropy is reduced less for the reaction intermediate than for the reactants, which leads to the lower barrier. SimulationsQuantum chemistry, the COSMO-RS implicit solvent model and statistical thermodynamics were employed to predict the stability of a range of reactants, catalysts and intermediates in a series of surfactant micelles. The localized stability in the linker region between the lipophilic and hydrophilic regions and the resulting decrease in entropy were also calculated. FindingsThe predicted reaction rates for the proposed mechanism show that the entropy reduction leads to a larger prefactor for the reaction. The resulting reaction rate can be significantly higher than conventional organic synthesis in an organic solvent even when the smaller reaction volume and lower reaction temperatures typically needed under micellar catalysis conditions are considered. The results are general across a wide range of types of reactions, reactants and catalysts and a selection of surfactants commonly used in organic synthesis, strongly supporting the hypothesis.

A Detailed Process and Techno-Economic Analysis of Methanol Synthesis from H2 and CO2 with Intermediate Condensation Steps

In order to increase the typically low equilibrium CO2 conversion to methanol using commercially proven technology, the addition of two intermediate condensation units between reaction steps is evaluated in this work. Detailed process simulations with heat integration and techno-economic analyses of methanol synthesis from green H2 and captured CO2 are presented here, comparing the proposed process with condensation steps with the conventional approach. In the new process, a CO2 single-pass conversion of 53.9% was achieved, which is significantly higher than the conversion of the conventional process (28.5%) and its equilibrium conversion (30.4%). Consequently, the total recycle stream flow was halved, which reduced reactant losses in the purge stream and the compression work of the recycle streams, lowering operating costs by 4.8% (61.2 M€·a−1). In spite of the additional number of heat exchangers and flash drums related to the intermediate condensation units, the fixed investment costs of the improved process decreased by 22.7% (94.5 M€). This was a consequence of the increased reaction rates and lower recycle flows, reducing the required size of the main equipment. Therefore, intermediate condensation steps are beneficial for methanol synthesis from H2/CO2, significantly boosting CO2 single-pass conversion, which consequently reduces both the investment and operating costs.

Pretreatment effect on copper-titanium dioxide catalysts in CO oxidation

Copper‑titanium dioxide (Cu-TiO2) catalysts are pretreated with hydrogen‑helium and oxygen‑helium before evaluation of the carbon monoxide oxidation. Pre-reduced Cu-TiO2 catalysts showed higher initial and overall activity than pre-oxidized Cu-TiO2 catalysts. H2-TPR results revealed that copper species are dispersed differently after pre-reduction and pre-oxidation treatments. XPS results confirmed that Cu+ and Cu2+ species exist for both treatments. Meanwhile, IR results suggested Cu+ species promote the absorption of CO, leading to increased reaction rates.