| Sustainable low-carbon future from current post-industrial civilization steer towards the ideal ecological civilization, underlies toughest energy challenges, as concern has risen over declining fossil fuel reserves and their detrimental effect on the environment. Thus clearly, it is vital from both economic and environmental points of view on finding alternative sources and promising routes to power the world. H2has long been considered as the environmentally friendly energy vector due to its zero-emissions nature and offers high energy efficiency. In particular considering, the on-board low temperature PEM(proton exchange membrane) fuel cell is potentially suggested as the primary choice for H2technology, for portable applications including heavy duty vehicles and small duty devices. Methanol steam reforming on demand for in-situ H2production is attracting significant interest, respect to its high volume and mass energy density values. However, the storage and transfer of H2in solid systems for mobil use are problematic because of poor volumetric and weight energy densities, accompany with the "Quick and Clean" requirements, the carbon monoxide must be minimised even with a tiny amount, while levels around10ppm in the gas stream will poison the PEMFC Pt electrode and severely impair its performance. The H2rich products from methanol steam reforming normally containing a molar concentration of0.5-2%CO in terms of a high conversion, and the followed cumbersome multistage CO post-treatments (like SELOX, WGS, Methanation, or Memberane Seperation) are always inapplicable. The utilization of H2(and CO2) directly without invoking any CO shift and clean-up stages to supply PEMFC is an attractive option, address this, it is aimed to develop a NSGDSR(non-syn gas direct steam reforming) process. Based on systematic screening and exploration, major conclusions and achievements are:1. A wide range of catalytic behaviour among catalysts prepared by co-precipitation, whilst on CuZnGaOx, not only have decent conversion for preferred activity, simultaneously also can minimising the CO which means with satisfied selectivity. The lower temperature and a faster substrate flow rate with a shorter contact time with the catalyst bed can significantly reduce the CO level, especially at150℃, this catalyst is able to achieve hydrogen productivity at a rate of393.6ml·g-1cat·hr-1and can totally suppress the CO production (below detection limit of1ppm) in a contact time of180s.kg-cat.mol-1, this is significantly better than the current industry standard:Johnson Matthey’s HiFUEL120commecial catalyst.2. The catalytic activity and selectivity are found to be critically dependent on copper surface area, catalyst structure and interaction, etc. SMS1(Strong Metal Support Interaction) favors a maximizing of copper dispersion and stability, by achieving a redox balance of the presence of Zn2+and interstitial Zn+.In a sharp contrast with CuZnOx and the identified CuZnGaOx for the pronounced difference in the SRM-NSGDSR. It is proposed that the gallium incorporation into copper-zinc oxide leads to the formation of NSS (non-stoichiometric spinel) cubic phase possess interstitial Cu which can in situ produce a high population of ultrafine5A Cu-cluster islands highly stabilized on defective NSS-ZnGa2O4surface upon controlled reduction. The introduction of trivalent Ga3+allows for variation of the concentration of free charge carriers, this result in the degradation of lattice oxygen mobility, but the spillover is promoted. thus the proportion of interface vacancies is increased alongside the decrease of isolated vacancies in support, which leading to enhanced Cu-surface area, and excellent reducibility below200℃, this in turn improves activity of NSGDSR process at low temperature.3. It is believed that there does exist a best point for ternary CuZnGaOx based on calculated atomic composition, including the factors such as copper loading, support combinations and even the synergistic effect. The SRM performances were investigated by contour maps of SAcat, conversion and CO with varies atomic content. It shows that the proportion of gallium is closely related to both activity and selectivity in opposite directions at195℃, and more gallium content favors better selectivity but with a poor activity, the location of quantified activity quite matches the SAcat contour map, whilst at150℃presence an offset towards high zinc content and all without CO formation. The best NSGDSR activity is found on CuZnGaOx with a molar ratio of43:47:10, and it is only the CuZnOx without gallium presence, on which appears to exist CO formation. Furthermore, coprecipitation pH. pre-reduction temperature and special additives can affect the catalytic activity under the premise of100%selectivity.4. Theoretical calculations were performed by using HSC Chemistry(?)5.11software, it is extreamly appreciated that SRM allows for below equilibrium concentration of CO on the working CuZnGaOx. On this basis, together with in situ DRIFTS, the mechanism was logically deduced, on CuZnOx it is impossible to inhibit trace CO formation derived from the decomposition of adsorbed formaldehyde intermediate, which can not be timely oxidized as the transient spillover absence of surface oxygen O+or hydroxyl, but on CuZnGaOx, CO formation can be sufficiently suppressed, by the greatly enhanced surface spillover with gallium whilst minimising the availability of vacancies in the bulk support, formaldehyde effectively converts into bidentate formate, which is generally considered to be the selective precursor for product CO2. Thus, further guaranteed the CO2selectivity, as NSGDSR is achieved at150℃on CuZnGaON, which is quite different from the former views.5. By adding a certain amount of oxygen to the methanol steam reforming system, but the hydrogen productivity is much lower during this auto-thermal process. Besides, the behavior on CO2hydrogcnation for methanol synthesis was studied to find the origin for the reaction, meanwhile undertake the comparable study with the reverse SRM reaction. |
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