Role of surface reconstruction on Cu/TiO2 nanotubes for CO2 conversion

Abstract

Carbon dioxide hydrogenation to CO via the reverse water gas shift (RWGS) reaction is one route to integrate CO 2 utilization into the chemical industry. TiO 2 supported Cu catalysts are known to be active for RWGS, but Cu is shown here to behave differently on TiO 2 nanotubes (TiNT) vs TiO 2 nanoparticles (TiNP). Whereas nanoparticle supports give low rates that are hardly changed by added Cu, the nanotube supports yield much higher activity and three distinct behaviors as the Cu surface density increases. At low surface densities (0.3 Cu/nm 2), active Cu-O-Ti sites are created that have low apparent activation energies. At high surface densities (6 Cu/nm 2), Cu nanoparticles on TiNT are formed, and reaction barriers are lowered when both Cu and TiNT surfaces are accessible. At intermediate surface densities, metallic Cu domains are engulfed by a TiOx overlayer formed during H 2 pretreatment, akin to those formed by classical strong metal support interactions (SMSI). These reduced layers are markedly more active for RWGS than the initial TiNT surfaces, but have similar activation barriers, which are higher than those for which both Cu and TiNP surfaces are exposed. These catalytic findings are supported by computational modeling, in situ IR, UV-visible, and X-ray absorption spectroscopies, and they provide insight into an important reaction for CO 2 utilization.

Ti3+ Tuning the Ratio of Cu+/Cu0 in the Ultrafine Cu Nanoparticles for Boosting the Hydrogenation Reaction

“…[38] The coexistence of Ti 3+ and Cu + from the XPS of reduced Ti-doped samples further suggest the formation of Ti 3+ O V Cu + bonds during the reduction of Ti 4+ OCu 2+ bonds. [39][40][41] Moreover, the ratio of Ti 3+ /(Ti 4+ +Ti 3+ ) in the three Ti-doped samples are similar, 41.2%, 39.6%, and 40.4% for Cu/ Ti(0.2)-SiO 2 , Cu/Ti(0.4)-SiO 2 , and Cu/Ti(0.6)-SiO 2 , respectively (Table S2, Supporting Information). Due to the similar sizes and dispersion of Cu nanoparticles among the three samples, the contact areas between Cu nanoparticles and the supports are similar, which leads to the similar proportion of Ti 4+ OCu 2+ bonds to be reduced.…”

Synthesis of oxygen vacancies enriched Cu/ZnO/CeO2 for CO2 hydrogenation to methanol

“…By comparing with the spectra of known compounds and published literatures, the assignment bands of adsorbed species were determined. A summary of assignments is listed in Table S3 17–19 . The carbonate species (1546, 1423, 1330, 1237, and 1085 cm −1 ), carbon ion (1072 cm −1 ), and formate (1595 and 1584 cm –1 ) for the CuZnCe catalysts can be observed in Fig.…”

Enhanced epoxidation of soybean oil by novel Al2O3–ZrO2–TiO2 solid acid catalyst

“…The spectrum of all samples showed strong absorption bands at 3430 cm −1 and 1636 cm −1 , attributed to the OH stretching and HOH bending modes of these groups on the surface of the nanoparticle. [ 44,45 ] Interestingly, the FT‐IR band at 3430 cm −1 arising from the surface OH group appeared to increase in intensity after Al 2 O 3 doping of ZrO 2 –TiO 2 , which is attributed to the vibrational modes of gibbsite and the stretching of hydrogen‐bonded hydroxyl groups in anatase TiO 2 with inter‐layer water molecules. [ 46–48 ] The results suggest partial transformation of the metal hydroxides to mixed oxides during calcination.…”