Adsorption and Polymerization of Formaldehyde on Cu(100)

Abstract

The adsorption of formaldehyde (H2CO) on clean Cu(100) at 85 K has been studied using electron energy loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD). For coverages up to (1.06 ± 0.22) × 1015 H2CO molecules/cm2, formaldehyde spontaneously polymerized to form a monolayer of disordered poly(oxymethylene) (POM), arranged with the chain directions parallel to the surface plane. Thermal decomposition/desorption of the polymer monolayer occurred by three routes, producing peaks in temperature-programmed desorption (TPD) at approximately 177, 200, and 215 K. The lowest temperature peak was exclusively associated with production of H2 and CO in approximately equal proportions. The two higher temperature peaks were produced by molecular H2CO generated via depolymerization of the polymer. The 200 and 215 K features displayed zero- and first-order desorption kinetics, corresponding to estimated activation energies for depolymerization of 75 ± 10 and 53.9 ± 0.5 kJ/mol, respectively. The presence of two polymer desorption peaks is attributed to chain conformational differences present within the monolayer and has not been previously observed in studies of formaldehyde adsorption on metal surfaces. Large exposures of H2CO on this surface formed multilayers of molecular formaldehyde on top of the first polymer layer. The second layer desorbed at 105 K and subsequent layers at ∼100 K.

Decomposition of Formaldehyde Multilayer Films on Deoxygenated, Oxygenated, and Water-Adsorbed Vanadium Substrates at Cryogenic Temperatures

“…The polymerization of H 2 CO is also observed on clean surfaces of Cu(110), 3,11 Ni(110), 9 Pd(111), 6 Pt(111), 4 and Zn(0001). 11 It has also been suggested that a methoxy intermediate is formed on Ni(110) 9 and Fe(100) 10 surfaces together with adsorbed CO and hydrogen. Oxygenation depresses the reactivity of Ru(001) for dehydrogenation of H 2 CO. 8 Reaction of H 2 CO with preadsorbed oxygen on Rh(111) forms CO, paraformaldehyde, formate, and η 1 -formaldehyde.…”

Bond Forming Reactions Involving C1 Moieties: Late Versus Early Transition Metal Surfaces

“…The conclusion is that coupling of formaldehyde adsorbates through their carbon ends takes precedent over any C-O bond-scission or dehydrogenation steps on the vanadium surface. The most common thermal chemistry seen for formaldehyde on transition metal surfaces has been its decomposition to carbon monoxide and hydrogen [15,72,75,[85][86][87][88][89][90][91], but diolate formation as reported here is known in homogeneous catalysis with titanium [92] and vanadium [93,94] low-valent compounds, and has also been reported on the surfaces of titanium [95] and uranium [96] oxides. The only other precedent for diolate formation on a metal is that reported on Mo(110) [86], another early transition metal.…”

Thermal reactions of mercaptoethanol on Cu(100)

“…Surface reactions of HSCH 2 CH 2 OH Fig. 1 shows the temperature-programmed reaction/desorption spectra of 1.5 L HSCH 2 CH 2 OH adsorbed on Cu(1 0 0) at 115 K, collected for the ions of 15,16,26,27,42,43, and 60 amu, representative of desorption of CH 4 , C 2 H 4 , CH 3 CHO, and HSCH 2 CH 2 OH. No HSCH 2 CH 2 OH molecular desorption, as shown in the 60 amu trace, is observed at 1.5 L exposure.…”

“…In the thermal decomposition of CH 3 OH on Cu(1 0 0), CH 3 Odecomposes to evolve CH 2 O between 370 and 450 K, however, -CH 2 O-surface intermediate is not detected by high-resolution electron energyloss spectroscopy (HREELS) [4]. Interaction between CH 2 O and Cu(1 0 0) has been investigated [15]. Upon CH 2 O adsorption on Cu(1 0 0) at 85 K, the molecules polymerize, forming poly (oxymethylene).…”