We have used spin polarized density functional theory calculations to perform extensive mechanistic studies of CO2 dissociation into CO and O on the clean Fe (100), (110) and (111) surfaces and on the same surfaces coated by a monolayer of nickel. CO2 chemisorbs on all three bare facets and binds more strongly to the stepped (111) surface than on the open flat (100) and close-packed (110) surfaces, with adsorption energies of -88.7 kJmol -1 , -70.8 kJmol -1 and -116.8 kJmol -1 on the (100), (110) and (111) (110) and (111) facets respectively. We have also investigated the thermodynamics and activation energies for CO2 dissociation into CO and O on the bare and Ni-deposited surfaces.Generally, we found that the dissociative adsorption states are thermodynamically preferred over molecular adsorption, with the dissociation most favoured thermodynamically on the closepacked (110) facet. The trends in activation energy barriers were observed to follow that of the trends in surface work functions; consequently, the increased surface work functions observed on the Ni-deposited surfaces resulted in increased dissociation barriers and vice versa. These results suggest that measures to lower the surface work function will kinetically promote the dissociation of CO2 to CO and O, although the instability of the activated CO2 on the Ni-covered 2 surfaces will probably result in CO2 desorption from the nickel-doped iron surfaces, as is also seen on the Fe(110) surface. Graphical abstract Introduction

Effect of nickel monolayer deposition on the structural and electronic properties of the low miller indices of (bcc) iron: A DFT study. Applied Surface Science 400 , pp.

Understanding the mechanism of CO2 reduction on iron is crucial for the design of more efficient and cheaper iron electrocatalyst for CO2 conversion. In the present study, we have employed spin-polarized density functional theory calculations within the generalized gradient approximation (DFT-GGA) to elucidate the mechanism of CO2 reduction into carbon monoxide and formic acid on the Fe (100) facet. We also sort to understand the transformations of the other isomers of adsorbed CO2 on iron as earlier mechanistic studies are centred on the transformations of the C2v geometry alone and not the other possible conformations i.e., flip-C2v and Cs modes. Two alternative reduction routes were considered i.e., the direct CO2 dissociation against the hydrogen-assisted CO2 transformation through formate and carboxylate into CO and formic acid. Our results show that CO2 in the C2v mode is the precursor to the formation of both products i.e., CO and formic acid. Both the formation and transformation of CO2 in the Cs and flip-C2v is challenging kinetically and thermodynamically compared to the C2v mode. The formic acid formation is favoured over CO via the reverse water gas shift reaction mechanism on Fe (100). Both formic acid formation and CO formation will proceed via the carboxylate intermediate since formate is a stable intermediate whose transformation into formic acid is challenging both kinetically and thermodynamically. Graphic abstract

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Insight into the detailed mechanism of the Sabatier reaction on iron is essential for the design of cheap, environmentally benign, efficient and selective catalytic surfaces for CO 2 reduction. Earlier attempts to unravel the mechanism of CO 2 reduction on pure metals including inexpensive metals focused on Ni and Cu; however, the detailed mechanism of CO 2 reduction on iron is not yet known. We have, thus, explored with spin-polarized density functional theory calculations the relative stabilities of intermediates and kinetic barriers associated with methanation of CO 2 via the CO and non-CO pathways on the Fe (111) surface. Through the non-CO (formate) pathway, a dihydride CO 2 species (H 2 CO 2), which decomposes to aldehyde (CHO), is further hydrogenated into methoxy, methanol and then methane. Through the CO pathway, it is observed that the CO species formed from dihydroxycarbene is not favorably decomposed into carbide (both thermodynamically and kinetically challenging) but CO undergoes associative hydrogenation to form CH 2 OH which decomposes into CH 2 , leading to methane formation. Our results show that the transformation of CO 2 to methane proceeds via the CO pathway, since the barriers leading to alkoxy transformation into methane are high via the non-CO pathway. Methanol formation is more favored via the non-CO pathway. Iron (111) shows selectivity towards CO methanation over CO 2 methanation due to differences in the rate-determining steps, i.e., 91.6 kJ mol −1 and 146.2 kJ mol −1 , respectively. Keywords Spin-polarized DFT-GGA • CO 2 methanation • CO methanation • Methanol formation • Reaction mechanism CO 2 + 4 H 2 → CH 4 + 2 H 2 O ΔH 298K = −252.9 kJ mol −1 .

The management of solid wastes at the workplace in Ghana is characterised by mixed wastes pickup delays, dustbin overflows and leakage of plastic bags into the environment. Benefits from the pilot of source sorting as a mitigation measure at the workplace are unavailable in literature. Hence, the study employed descriptive statistical tools to assess the advantages of a piloted source sorting system at the CSIR-IIR. The sampled size was 100 staff with an 80% questionnaire recovery rate. The analysis of data showed that, the implementation of segregation at source transformed the social approach of workers towards waste management. Most workers (97.7%) preferred sorting their wastes at source irrespective of the location of the generation point. A congenial environment was created by the source separation infra­structure, which made staff worked better, (70% responses). The majority of staff (95.2%) confirmed the savings made by the Institute on the cost of landfilling. The sorting at source improved cleanliness of the compound (97.6% responses) and eliminated open-air burning of wastes (95.1% responses). In all, the source segregation was beneficial to the social, economic and environmental well-being of staff and management of the Institution.

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