Tracking Site-Specific C–C Coupling of Formaldehyde Molecules on Rutile TiO<sub>2</sub>(110)

Zhu, Kun Yan; Xia, Yaobiao; Tang, Miru; Wang, Zhitao; Jan, Bryan; Lyubinetsky, Igor; Ge, Qingfeng; Dohnálek, Zdenek; Park, Kenneth T.; Zhang, Zhenrong

doi:10.1021/acs.jpcc.5b04781

Cited by 22 publications

(49 citation statements)

References 31 publications

(114 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…25,26 Scanning tunneling microscopy (STM) images have directly visualized that formaldehyde preferentially adsorbs on V O sites, which agrees with the ensemble-averaged experimental studies, 18,23 but are at odds with the theoretical results. 19,25 …”

Section: ■ Introductionsupporting

confidence: 68%

“…These hydroxyls are stationary during the whole processes as expected at 215 K. 26 It is worth noting that the formation of V O −CH 2 is different from the previously reported diffusion of CH 2 O b , which diffuses as an intact molecule to and along the Ti row ( Figure 2a′). 25 Here the diffusion of the CH 2 species indicates the direct breaking of the C−O bond in formaldehyde, which has not been reported before on oxides.…”

Section: ■ Experimental Sectionsupporting

confidence: 50%

“…27 As reported in our previous study, most of Ti-bound CH 2 O Ti adsorbed on V O appear as a fuzzy CH 2 O b feature as marked by the arrows. 25,26 In addition, the coupling of CH 2 O Ti with CH 2 O b has been shown to lead to O b CH 2 CH 2 O Ti diolate (circle), which is brighter than CH 2 O b and is centered between the Ti row and the O b row. 26 In Figure 1a 25 An alternate diffusion channel, which is the diffusion from V O to and along Ti row as intact molecules occurs at higher temperatures (>210 K) and should be accompanied by the appearance of the V O sites, and therefore, it is not considered here.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…There is only a small amount of the reaction product, diolate (<0.01 ML), which is expected because of the low probability of CH 2 O Ti reacting with newly formed CH 2 O b during the exposure. 26 The probability of CH 2 O b encountering each other, reacting, and desorbing as ethylene increases at temperatures above 215 K since CH 2 O b can diffuse along the O b row as CH 2 group with an estimated diffusion barrier (E b ) of 0.4−0.5 eV. 25 The probability of this reaction is proportional to the concentration of the CH 2 O b molecules that are near to each other.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

See 3 more Smart Citations

Low-Temperature Reductive Coupling of Formaldehyde on Rutile TiO₂(110)

et al. 2015

Self Cite

View full text Add to dashboard Cite

The formation and coupling of methylene upon dissociation of formaldehyde on reduced TiO 2 (110) are studied using variable temperature scanning tunneling microscopy (STM). In agreement with prior studies, formaldehyde preferably adsorbs on the bridging-bonded oxygen vacancy (V O ) defect site. V O -bound formaldehyde couples with Ti-bound formaldehyde forming a diolate species, which appears as the majority species on the surface at 300 K. Here, STM images directly visualize a low-temperature coupling reaction channel. Two V O -bound formaldehyde molecules can couple and form Tibound species, which desorbs above ∼215 K. This coupling reaction heals both V O sites indicating the formation and the desorption of ethylene. We also directly observed the diffusion of methylene groups to nearby empty V O sites upon dissociation of the C−O bond in V O -bound formaldehyde, which suggests that the ethylene formation occurs via coupling of the methylene groups. Statistical analysis shows that the sum of visible reaction products on the surface can only account for a half of the consumption of the initial V O coverage, which further supports the desorption of the coupling reaction product, ethylene, after formaldehyde exposure between 215 and 300 K. ■ INTRODUCTIONChemical reactions of aldehyde on reducible metal oxides are important in numerous catalytic reactions in the applications related to the degradation of toxic compounds, air purification, and chemical synthesis. 1−3 For instance, reductive coupling of carbonyl species has proven to be a versatile strategy for the functionalization of vicinal carbon atoms in organic molecules. 3−5 Adsorption and reaction of various oxygenated hydrocarbons on well-defined surfaces have been extensively studied to provide unparalleled understanding of the reaction mechanisms. 6−10 Production and conversion of simple C1 molecules such as methane, methanol, formaldehyde and formic acid are involved in many of these reactions. Hence the reactivity of formaldehyde has been studied on many metal 11−17 and metal oxide surfaces 18−24 . On metal surfaces, formaldehyde generally dehydrogenates to form CO via various intermediates such as formyl, methoxy, and formate. The coupling of aldehydes to form alkenes has been identified on TiO 2 , 6,9,18,23 UO 2 , 20 V(100), 11 and Mo(110). 12 On these surfaces, the coupling reaction proceeds through the formation of diolates via C−C coupling of two aldehydes. 6,9,12,18,20 A distinct low-temperature pathway was determined on V(100), which occurs via the coupling of methylene groups formed upon dissociation of the C−O bond in adsorbed formaldehyde. 11 On reduced TiO 2 (110) surfaces, several ensemble-averaged experimental studies reported the C−C coupling of CH 2 O forming a diolate (−OCH 2 CH 2 O−) species, followed by ejection of the olefin at high temperature (∼600 K). 18,23 There is currently a controversy regarding the role of the defects including the bridging-bonded oxygen (O b ) vacancy (V O ) and Ti interstitial in this coupling reaction. 6,18,...

show abstract

Section: ■ Introductionsupporting

confidence: 68%

Section: ■ Experimental Sectionsupporting

confidence: 50%

Section: ■ Experimental Sectionmentioning

confidence: 99%

Section: ■ Experimental Sectionmentioning

confidence: 99%

See 2 more Smart Citations

Low-Temperature Reductive Coupling of Formaldehyde on Rutile TiO₂(110)

et al. 2015

Self Cite

View full text Add to dashboard Cite

show abstract

“…The adsorption and reactions of CH 2 O on TiO 2 surfaces have been extensively studied both experimentally and theoretically [16][17][18][19][20][21][22][23][24][25][26][27][28][29]. It has been well-established that CH 2 O can adsorb on TiO 2 surfaces in two different configurations [19, 21-23, 25, 28, 29].…”

Section: Introductionmentioning

confidence: 99%

Photoinduced decomposition of formaldehyde on rutile TiO2(100)-(1×1)

Xiao

Guo

et al. 2018

Chinese Journal of Chemical Physics

View full text Add to dashboard Cite

We have investigated the photoinduced decomposition of formaldehyde (CH 2 O) on a rutile TiO 2 (100)-(1×1) surface at 355 nm using temperature-programmed desorption. Products, formate (HCOO −), methyl radical (CH 3 •), ethylene (C 2 H 4), and methanol (CH 3 OH) have been detected. The initial step in the decomposition of CH 2 O on the rutile TiO 2 (100)-(1×1) surface is the formation of a dioxymethylene intermediate in which the carbonyl O atom of CH 2 O is bound to a Ti atom at the five-fold-coordinated Ti 4+ (Ti 5c) site and its carbonyl C atom bound to a nearby bridge-bonded oxygen (O b) atom, respectively. During 355 nm irradiation, the dioxymethylene intermediate can transfer an H atom to the O b atom, thus forming HCOO − directly, which is considered as the main reaction channel. In addition, the dioxymethylene intermediate can also transfer methylene to the O b row and break the C−O bond, thus leaving the original carbonyl O atom at the Ti 5c site. After the transfer of methylene, several pathways to products are available. Thus, we have found that O b atoms are intimately involved in the photoinduced decomposition of CH 2 O on the rutile TiO 2 (100)-(1×1) surface.

show abstract

Imaging Chemical Reactions One Molecule at a Time

Novotný¹,

Zhang²,

Dohnálek³

et al. 2018

Encyclopedia of Interfacial Chemistry

View full text Add to dashboard Cite

In this article, we focus on demonstrating the utility of scanning probe methods in the imaging of chemical reactions. We first highlight the utility of different imaging methods and highlight their advantages and drawbacks. Subsequently, we select a number of examples to illustrate different surface processes including adsorption, dissociation, diffusion and rotation of adsorbed molecules, formation of reaction intermediates, and conclude with complex reactions. In these examples, we mainly focus on the STM, which is most extensively employed as a method of choice. To limit the complexity of the article we have selected only a few systems for the discussion. In particular, elemental steps in the reactions of water, alcohols, and diols on TiO2(110) surface are utilized to illustrate the power of imaging techniques in our understanding of surface chemistry. We also provide a brief outlook on both current and future challenges in this exciting area of research.

show abstract

Tracking Site-Specific C–C Coupling of Formaldehyde Molecules on Rutile TiO₂(110)

Cited by 22 publications

References 31 publications

Low-Temperature Reductive Coupling of Formaldehyde on Rutile TiO₂(110)

Low-Temperature Reductive Coupling of Formaldehyde on Rutile TiO₂(110)

Photoinduced decomposition of formaldehyde on rutile TiO2(100)-(1×1)

Imaging Chemical Reactions One Molecule at a Time

Contact Info

Product

Resources

About

Tracking Site-Specific C–C Coupling of Formaldehyde Molecules on Rutile TiO2(110)

Cited by 22 publications

References 31 publications

Low-Temperature Reductive Coupling of Formaldehyde on Rutile TiO2(110)

Low-Temperature Reductive Coupling of Formaldehyde on Rutile TiO2(110)

Photoinduced decomposition of formaldehyde on rutile TiO2(100)-(1×1)

Imaging Chemical Reactions One Molecule at a Time

Contact Info

Product

Resources

About

Tracking Site-Specific C–C Coupling of Formaldehyde Molecules on Rutile TiO₂(110)

Low-Temperature Reductive Coupling of Formaldehyde on Rutile TiO₂(110)

Low-Temperature Reductive Coupling of Formaldehyde on Rutile TiO₂(110)