10The mechanism of CO2 reduction by H2 at atmospheric pressure was investigated on 11 Ru(0001) by coupling density functional theory (DFT) calculations with mean-field 12 microkinetic modeling. The initial CO2 hydrogenation step leading to CH4 production was 13 shown to occur through CO2 dissociation and subsequent hydrogenation of CO* to CHO*. 14 The dissociation of CHO* to form CH* and O* was identified as the rate limiting step for CH4 15 formation, while the rate limiting step for CO production through the reverse water gas 16 shift reaction was identified as CO* desorption. Based on a scaling relations analysis of 17 competing CHO* dissociation and CO* desorption, O* adsorption energy was found to be an 18 effective descriptor of differences in selectivity between CO and CH4 production previously 19 observed on late-transition metal catalysts. These mechanistic insights provide critical 20 information to guide the design of catalysts with tunable selectivity for CO2 reduction by H2 21 at atmospheric pressure. 22 1. Introduction 1 More than 85% of the current global energy need is provided by combustion of 2 fossil fuels, which is accountable for continuously increasing atmospheric concentrations of 3 CO2 and accompanying climate change effects.[1] The search for approaches to reduce 4 atmospheric CO2 concentration has become a high priority research area. Recent efforts 5show the potential promise of directly sequestering CO2 from the atmosphere using amine 6 based sorbent materials, among other methods. [2][3][4][5][6] If approaches to directly sequester 7 CO2 from the atmosphere prove successful, it will be important to develop efficient, low 8 temperature and pressure processes for converting CO2 to higher value hydrocarbon 9 feedstocks for chemical and fuel production. The coupling of CO2 sorption technologies 10 with solar-based H2 production through catalytic reduction processes would provide an 11 energy efficient, environmentally friendly and carbon neutral approach for chemical and 12 fuel production. This approach relies, in part, on the development of materials that 13 facilitate catalytic conversion of CO2 and H2 into desired products with high selectivity.14 Because of high energy requirements, C-C coupling reactions are rare at low 15 temperature and pressure and it is expected that C1 molecules (CO, CH3OH and CH4) will be 16 the dominant products of environmentally friendly CO2 reduction processes. CH3OH 17 synthesis from CO2 and H2 on Cu and "Cu-like" catalysts has received significant attention, 18 due the extensive use of CH3OH as a precursor for production of chemicals and liquid fuels. 19However, CH3OH is a minimal side product under low pressure CO2 hydrogenation 20 conditions.[7-9] On the other hand, highly selective catalytic CH4 and CO production has 21 been demonstrated at low temperature (as low as 150 • C) and atmospheric pressure over a 22 range of supported transition metal catalysts (eg. Ni, Ru, Rh, Pd, Pt).[10-15] Supported Ru and Rh catalysts are consistently observed to...
Catalytic dehydration of ethanol is a key step in the production of polyethylene from renewable raw materials. Obtaining a mathematical model to optimize the ethanol-to-ethylene reactor setup is of great interest to the industry, allowing the optimal design of larger plants and improvements to existing plants. This work presents a phenomenological model of an ethanol dehydration reactor that takes into account 8 chemical reactions and 10 chemical species, considering nonidealities in the reaction rates and axial catalyst activity profile. Additionally, the axial variation of pressure, velocity, and thermodynamics properties are considered in the proposed model. Model validation at different operating conditions shows that the predicted temperature and composition profiles match the data from an industrial plant with relative deviations below 5% and from a pilot plant with relative deviation below 0.4%.
Recent approaches for the rational design of heterogeneous catalysts have relied on first-principles-based microkinetic modeling to efficiently screen large phase spaces of catalytic materials for optimal activity and selectivity. Microkinetic modeling allows the calculation of catalytic rate and selectivity under a given set of conditions without a priori assumptions of rate or selectivity controlling steps by simultaneously solving nonlinear algebraic equations comprising species mass balances bound by the pseudo steady-state approximation. We introduce a general approach to define and solve microkinetic systems that relies solely on its stoichiometric matrix and kinetic parameters of considered reaction steps. Our approach relies on linearization of the microkinetic system, enabling analytical calculation of system derivatives for use in quasi-Newton solution schemes that exhibit excellent robustness and efficiency with minimal dependence on initial conditions.To develop a general approach for solving complex microkinetic systems, we start by defining all species in the system as S j 's rather than p j 's and h j 's. The rate equations Scheme 1. Three-step catalytic mechanism. Scheme 2. Reactions rate equations.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.