Probing active species for CO hydrogenation over ZnCr2O4 catalysts

Oxygen-Defect-Mediated ZnCr2O4/ZnIn2S4 Z-Scheme Heterojunction as Photocatalyst for Hydrogen Production and Wastewater Remediation

“…The O 1s spectrum (Figure e) can be divided into three peaks located at 530.2, 531.4, and 532.6 eV, which are assigned to lattice oxygen (O latt ) inside the sample, adsorbed oxygen (O ads ) on the surface, and H 2 O molecules, respectively . It has been generally recognized that the characteristic peak at 531.4 eV signifies the possible existence of oxygen vacancy defects in the structure of ZnCr 2 O 4 . The presence of abundant oxygen vacancies will form a defective energy level that is able to greatly improve the photocatalytic performance of ZnCr 2 O 4 . , It is worth noting that the relative intensity values of the O ads peak to the O latt peak in the ZCO-ZIS-0.6 composite sample are substantially higher than those in the ZnCr 2 O 4 sample, suggesting that the relative concentration of oxygen vacancies in the composite increases sharply, which should be related to the employment of the strongly reducing glycerol in the compositing experiment.…”

“…Seeking for semiconductors matching the energy band of ZnIn 2 S 4 to construct heterojunctions has become a vital strategy to improve the photocatalytic performance and photostability, such as MoO 3 /ZnIn 2 S 4 , ZnS/ZnIn 2 S 4 , PCN-224/ZnIn 2 S 4 , g-C 3 N 4 /ZnIn 2 S 4 , and so on. ZnCr 2 O 4 is a typical chromium-based spinel semiconductor, which has shown broad applications in gas sensing, humidity sensing, syngas conversion, and adsorption . Unfortunately, the large energy band width leads to the fact that ZnCr 2 O 4 can only be excited by UV light.…”

In Situ Restructuring of ZnCr2O4 Spinel Catalyst Alters Elementary Surface Reaction Kinetics and Catalytic Selectivity in CO Hydrogenation Reaction

“…13 CO activation on a ZnCr 2 O 4 surface with hydroxyl groups was observed to form carbonates while CO activation occurred on a ZnCr 2 O 4 surface with surface hydride species to form formate species. 10 CO dissociation was observed on prereduced ZnCrO x 2 and ZnCrO x -Al 2 O 3 14 catalysts to form atomic C species, accompanied by gaseous CO 2 . The resulting C adatoms were observed to be capable of facilely hydrogenating into hydrocarbons at 673 K and above.…”

“…The in situ DRIFTS spectra of the ZnCr 2 O 4 catalyst under the steady-state CO hydrogenation reaction (H 2 :CO = 2, P = 2.5 MPa) at 573 and 673 K were measured. The observed vibrational bands were assigned and summarized in Table S1 based on previous results. ,,,− At 573 K (Figure a), vibrational features of various surface species including bridged formate at the Zn-Cr site (denoted as (Zn,Cr)-bri-HCOO*) and Zn–Zn site (denoted as (Zn,Zn)-bri-HCOO*), monodentate formate (m-HCOO*), methoxy (CH 3 O*), adsorbed CH 3 OH* and bicarbonate (HCO 3 *), and gaseous CH 4 were observed. The formate, methoxy, and adsorbed CH 3 OH species were typical surface intermediates for CO hydrogenation to methanol, while the bicarbonate species was the surface intermediate for CO 2 production.…”

“…15−17 Zn-Cr oxide catalysts are expected to restructure under the reducing syngas atmosphere with high pressures and at high temperatures; thus, studies of activation and surface reaction of CO and H 2 on Zn-Cr oxide catalysts need to be conducted under the working conditions to acquire A spinel ZnCr 2 O 4 catalyst was prepared via a previously reported coprecipitation method. 10 Its catalytic performance in the CO hydrogenation reaction was evaluated as a function of reaction temperature. As summarized in Table 1, the CO conversion was 3.5% at 543 K and steadily increased to 6.1% at 573 K; meanwhile, the dominant product was CH 3 OH with selectivity above 85% and minor products included CH 3 OCH 3 , CO 2 .…”