Hartmut Hobert

Thermal desorption and infrared studies of butylamine adsorbed on SiO2, Al2O3 and CaO

The adsorption of n-butylamine on SiO2, γ-Al2O3 and CaO at the solid/vapour interface has been studied by infrared spectroscopy and temperature-programmed desorption(t.p.d.) The infrared spectroscopic results show that adsorption of n-butylamine on SiO2 leads to the formation of hydrogen bonds between surface hydroxy groups and amine molecules. Adsorption on γ-Al2O3 and CaO involves coordinative interactions between amine molecules and Lewis-acidic surface sites (Al3+ and Ca2+ cations), but hydrogen bonding also occurs. In the t.p.d. spectra one (SiO2) or two (Al2O3, CaO) strong maxima appear caused by the desorption of n-butylamine and butyronitrile, respectively. Desorption of unchanged butylamine at low temperatures can be attributed to amine molecules hydrogen-bonded to surface hydroxy groups of the oxides. However, there are some phenomena which indicate the possibility that molecules coordinatively bonded to weak Lewis-acidic surface centres contribute to this maximum. On the other hand, only butylamine molecules coordinatively bonded to strong Lewis-acidic centres are dehydrogenated and desorb as butyronitrile at higher temperatures.

Thermal desorption and infrared studies of amines adsorbed on SiO2, Al2O3, Fe2O3, MgO, and CaO II. Isopropylamine and cyclohexylamine

Abstract The adsorption of isopropylamine and cyclohexylamine on Al 2 O 3 and Fe 2 O 3 , and of isopropylamine on SiO 2 , MgO, and CaO has been studied by infrared spectroscopy and temperature-programmed desorption (TPD). Surface complexes are formed at beam temperature as a result of hydrogen bonding and dissociative adsorption on SiO 2 , and formation of coordination bonds between amine molecules and Lewis-acidic surface sites on the other oxides. With increasing temperature during TPD, in addition to the unchanged amines, products desorb, which indicates the occurrence of Cue5f8N bond breakage and dehydrogenation reactions.

Thermal desorption and infrared studies of primary aliphatic amines adsorbed on haematite (α-Fe2O3)

The adsorption of n-octadecylamine on α-Fe2O3 at the solid/liquid interface, and of n-butylamine at the solid/liquid and solid/vapour interfaces has been studied by infrared spectroscopy. To obtain further information about the nature of desorbing products, temperature-programmed desorption experiments were made with n-butylamine–α-Fe2O3 absorbates. No difference could be detected by i.r. spectroscopy between the nature of adsorbates formed under the various mentioned conditions. Adsorption of n-octadecylamine and n-butylamine on α-Fe2O3 mainly involves coordinative interactions between amine and Lewis-acidic surface sites (Fe3+ cations). Furthermore, hydrogen bonds are formed between surface hydroxy groups and adsorbed amine molecules. n-Butylamine adsorbed on α-Fe2O3 gave four different desorption peaks (I–IV) which are formed by n-butylamine (I: 423 K), butyronitrile (II: 530 K), CO2(III: 630 K) and H2O (IV: 713 K). Desorption of CO2 and H2O is caused by the oxidation of amine molecules strongly adsorbed on two different types of coordination sites.

Adsorption of nickeltetracarbonyl on zeolites studied by infrared spectroscopy

Ni(CO)4 is adsorbed on wide pore X and Y zeolites inside the pores of the zeolites and shows a set of strong bands between 2,150 and 1,950 cm−1. Only one kind of adsorbed Ni(CO)4 exists on NaX zeolite, whereas two species of adsorbed Ni(CO)4 with C2v and C3v symmetry exist on NaY and NaHY zeolites. The concentration ratio of both carbonyls depends on the Na+H+ exchange ratio. Ni(CO)4 is physisorbed on narrow pore A and ZSM-5 zeolites on the outer surface producing a small band at 2,058 cm−1 with a shoulder at 2,040 cm−1. The appearance of some other small bands individual for each sample suggests an adsorption on structural defects and a partial decomposition of the carbonyl.

Infrared study of the adsorption of octadecylamine at the MgO/CCl4 interface. A comparison with investigations of the adsorption of octadecylamine on SiO2 and Al2O3

The adsorption of octadecylamine on highly dispersed magnesium oxide immersed in carbon tetrachloride has been studied by infrared spectroscopy. No difference could be detected between infrared bands appearing in the spectra of MgO in situ immersed in the pure solvent after contact with the solution of octadecylamine and MgO drained and evacuated at beam temperature. Adsorption of octadecylamine on MgO involves coordinative interactions between amine and Lewis-acidic surface sites. The results are discussed in comparison with those for the adsorption of octadecylamine at the SiO2/CCl4 and Al2O3/CCl4 interfaces.

Application of Principal Component Analysis to the Studies of OH Groups in NaHY Zeolites

The Si-OH-Al bridging hydroxyls in zeolites are active sites in many important reactions catalyzed by zeolites. Their amount and their acid strength have been extensively studied in many laboratories (for reviews see Refs. 1 and 2). We undertook studies of the heterogeneity of Si-OH-Al groups in zeolites, i.e., the presence of a few kinds of bridging hydroxyls of various acid strength in the same zeolite structure. We studied the heterogeneity of OH groups in NaHZSM-5 zeolites, NaHA zeolite, and NaH faujasites.