TITLE:
A method to make CuO/ZnO/Al2O3 Ternary Catalyst for Methanol Synthesis
Field of Invention
The present invention relates to a process for preparing ternary CuO/ZnO/Al2O3 catalyst for methanol
synthesis.
Background of the invention:
Methanol is one of the most important basic chemicals in chemical industry. It is
produced from synthesis gas (carbon monoxide and hydrogen), and syngas itself is derived
from oil, coal or, increasingly, biomass.
The largest use for methanol is as a feedstock for the plastics industry. It is used to
make methanol and hence a variety of plastics, based on reactions with phenol, carbamide
(urea) and melamine. Polymers such as the polyesters (e.g. Terylene)and poly (methyl-2-
methylpropenoate) (e.g. Perspex) use methanol as the original feedstock. Methanol is now
the principal source for the manufacture of ethanoic acid.
In industry, methanol is produced from H2, CO, and C02 - synthesis gas. These gasses
react in the presence of Cu/ZnO/Al2O3 catalytic systems, temperatures of 250 - 350 'C and
pressures of up to 100 atm. Modern production plants achieve up to 5000 tons per day of
methanol. The present invention is related to the catalyst making procedure for methanol
production for industrial applications.

The hydrogenation step can occur on both carbon monoxide and carbon dioxide, as can be
seen in the following reactions (1) & (2). The production and use of methanol is a "climate
neutral" reaction - the carbon monoxide used in the reaction is re-emitted during
combustion. Other promising synthesis routes start with methane (oxidation) or pure carbon
dioxide (reduction). Both substances are known as "greenhouse gasses," and the possibility
to economically convert them is strongly desired.
CO+2H2 <-> CH3OH (1)
CO2 + 3H2 <-> CH3OH + H2O (2)
From considering the energetics of the reactions, the yield of methanol is favored by
high pressures and low temperatures [l]. A low-pressure process came about by the
discovery of a copper-based catalyst which was active at 475-575 K, thus allowing
economical conversions to occur at 40-100 atm.
The process for the making of an industrial catalyst for methanol production broadly has
the steps outlined in figure 1. Cu/ZnO/AI2O3 catalysts have been applied for nearly 50 years
, in methanol synthesis, a large-scale industrial process of still growing importance with a
current demand of more than 60 million metric tons per year. Particularly in the context of a
sustainable future energy system, methanol produced from CO2 and H2 is believed to play a
vital role as an energy storage molecule. Though the history is long, there has not been a real
understanding of the nature of active sites and the exact mechanism for many years. They
were for a long time a matter of strong debate.

Where some argue that metallic Cu0 is the active site[2,3J, others make out Cu0
dissolved in ZnO, stabilized by promoters as active sites[4,5]. It is also suggested that Cu~ at
the Schottky junction, the interface of Cu metal and ZnO, is the active site [6,7]. The Topsoe
model [8] supports the idea of a strong metal support interaction (SMSI) [9,10]. Under
reducing conditions, Zn atoms migrate onto the copper surface. Behrens et al. [11J report in
a study which combines experimental evidence and theoretical prediction that a stepped Zn
decorated Cu surface are the active sites for the methanol synthesis from a CO2 containing
feed. Today it is agreed upon that ZnO acts as a structural promoter. As spacers, ZnO
particles inhibit the sintering of the copper particles and enhance copper dispersion.
Therefore the copper surface area is increased leading to a likewise increase in catalytic
activity. However, as it was found out that the activity of Cu/ZnO catalysts is not linearly
increasing with the copper surface area, ZnO also seems to play a role in the formation of
active sites. One reason that made it so difficult to compare activities and other
characteristics of the catalysts and draw a clear conclusion regarding active sites is the strong
dependence of the catalysts on their precursors. This influence is often termed the chemical
memory of the catalyst system [12].
The most relevant route for the preparation of highly active catalysts is coprecipitation
of the metal nitrates (copper, zinc, aluminum nitrates) with sodium carbonate in a way that the
pH of the slurry remains constant (13]. The coprecipitation is done by adding metal and
carbonate solution simultaneously to a separate reactor vessel. For the ternary system,
optimum preparation conditions were found at a reaction temperature of 338 K and nearly
neutral pH of 6.5-6.8 [14,15].
Various precursor preparation parameters, especially of the early stages of precipitation
and aging such as pH, temperature, aging time next to the chemical composition were found to
influence the properties of the final catalyst strongly.

The conditions determined to yield the best catalyst can be reasoned in terms of leading
to the best inter dispersion of copper and zinc atoms and a favorable microstructure in the solid
precursor. In the present study, we wanted to do away with the drop by drop addition of metal
nitrates and alkali carbonate into the reaction chamber.
Instead of a drop by drop reaction process in the chamber where alkali carbonate and
metal nitrates are added separately, the present invention used a one pot synthesis approach
using microwaves as the heating source. Further steps in the catalyst making were carried out
in the similar ways as has been mentioned in the literature. The major advantage of this
, process is that the heating is uniform throughout the catalyst precursor. Hence, the formation
of the precipitates is uniform at any given point of time. In essence, the nature of the precursor
mixture which determines the quality of the final catalyst could be controlled when microwave
irradiation is used.
Objects of the invention:
An object of the present invention is to propose a process for preparing ternary CuO/ZnO/AI2O3
catalyst for methanol synthesis wherein microwave irradiation is used during the co-precipitation step.
Another object of the present invention is to use the ternary CuO/ZnO/AI2O3 catalyst for methanol
synthesis.
Summary of the invention:
A process for preparing ternary CuO/ZnO/AI2O3 catalyst for methanol synthesis comprising:
subjecting the nitrates of Cu, Zn, and magnesium to the step of Co precipitation using microwave
Irradiation,
ageing the precipitates in a microwave at a temperature between 50 to 250<>C.

filtering the precipitate to form a filtered cake
drying and crushing the filter cake to form the precusor
subjecting the precusor to the step of calcination to form oxides of cu, zn and
reducing the copper oxides in situ to form the active catalyst.
A brief description of accompanying figures:
• Figure 1 shows the various steps in the process of making a ternary catalyst.
• Figure 2 shows the XRD analyses of the catalyst powder which used microwave irradiation
for co-precipitation
• Figure 3 shows the XRD analysis of the catalyst powders after calcination step.
• Figure 4 shows the SEM analysis of the catalyst powder after ball milling for 4 hours using
zirconia vessels and balls.
Detailed description of the Invention:
The present invention utilizes the microwaves for the co-precipitation step in the preparation of
the ternary catalyst Cu/ZnO/Al2O3. This process helps in uniform heating of the catalyst
precursor solution, and hence each area throughout the catalyst is subjected to similar conditions
resulting in the uniformity during co-precipitation.

Commercially, CuO/ZnO/Al2O3 catalysts are prepared by co-precipitation method in stirred tank reactors using aqueous solutions of metal nitrates and sodium carbonate to generate mixed
Cu/Zn/Al hydro carbonate precursors, followed by calcination and reduction processes to form
the active Cu/ZnO/Al2O3 catalysts. Constant pH condition is required in the catalyst synthesis to
avoid independent or sequential precipitation of Cu2+ and Zn2+, which prevents the
homogeneous distribution of both species in the precipitate. Additionally, other conditions like
temperature, reactant concentration and stirring speed will also play significant roles on the
physicochemical properties of the precursors and, in turn, the catalytic activity of the final
catalysts. However, it is hard to precisely control this big set of parameters for one particular
precipitation process in traditional stirred reactors. The present invention wants do away with the
use of stirred tank reactors for co-precipitation method and instead use microwave irradiation for
the same.
A representative embodiment of the methods is to take the nitrates of copper, zinc and/or
magnesium and other optionally at least one element selected from aluminum, vanadium,
chromium, titanium, zirconium, manganese, molybdenum and/or silicon and subjecting them to
reducing conditions so that the copper and zinc components are reduced to their oxides in a
microwave digestion system. Further in the embodiment of the process is to age the precipitate
obtained during the reduction process at temperatures below 250 oC for a time above 3hours
under continuous stirring in a microwave. The cake left after the filtrate is removed is further
dried and washed to remove any excess of the reducing agents still present. The dried precursor
powder is subjected to calcination to make an intimate mixture of copper oxide, zinc oxide
and/or oxides of the other added elements. Finally, the obtained powder is subjected to ball
milling for 4 hours for even mixing of the oxides and also for reducing the particle size as the
powder gets agglomerated during calcination.

Example
Co-precipitation: Copper nitrate - 16g, Zinc nitrate - 8g, Magnesium Nitrate - 0.5 g, Alumina
• sol -10g, Potassium carbonate -13g
300 ml of DI water with 10 ml of alumina sol was heated to 70 'C, and the nitrates of the
metals (16g of copper nitrate, 8 g of zinc nitrate and 0.5 g of magnesium nitrate) were added
after reaching 70 'C. Further, 13g of potassium carbonate was added in 100 ml of DI water in a
separate vessel and stirred continuously. The carbonate solution was added into the metal nitrate
solution and allowed the metals to co-precipitate in a microwave digestion system for 3hours at a
set temperature of 130 oC. Further, the stirring was continued for the precipitates to age for 3
hours in the microwave. Later, the precipitate was filtered and the precipitate cake was dried at
110 C for 3 hrs in a regular oven. The filtered cake turned from a light blue to green color which
is an indication of loss of moisture. The dried mass is crushed with mortar pestle until visible
chunks of the powder are converted into powder form. XRD analysis for the obtained precursor
powder is done.
Calcination:
The next step is a calcination step. For this, the crushed powder is heated at 350 C for 3.5
hours. The resultant powder is black in color. The powder was then subjected to ball milling in
zirconia vessels and balls for 4 hours to reduce the particle agglomeration during the calcination
step. The XRD analysis of the powder is shown in figure 3. A SEM image of the powder
showing the particle morphology as near spheres and a particle size between 30-60nm is
provided in figure 4.

As can be clearly seen in the XRD analysis, several complex phases such as copper
nitrate hydroxide, hydrotalcite, etc. were formed during the co-precipitation process. The phase
of copper or zinc nitrate hydroxide are formed since the nitrate, and hydroxyl metal compounds
are easy to precipitate than the carbonate metal compounds due to the lower concentration of
CO32-, thus CO32- did not present in the precursor but coordinated to form the phase of nitrate
hydroxide phase.
We can see that after the calcination, the phases of oxides of Copper, Zinc, and
Aluminum are formed. The largest two peaks of CuO correspond to the (002) and (200) planes.
In situ reduction of copper oxide inside the reaction chamber is necessary before the catalyst
starts turning syngas to methanol. For that, a series of hydrogen treatment is required. As the
lumps formed after calcination were large, one ball milling step for 4 hours was carried out to
reduce the particle size. The final particle sizes varied between 30-50 nm as can be seen in the
SEM image.

WE CLAIM
1. A process for preparing ternary CuO/ZnO/Al2O3 catalyst for methanol synthesis comprising:
subjecting the nitrates of Cu, Zn, and magnesium to the step of Co precipitation using
microwave irradiation,
ageing the precipitates in a microwave at a temperature between 50 to 250°C.
filtering the precipitate to form a filtered cake
drying and crushing the filter cake to form the precusor
subjecting the precusor to the step of calcination to form oxides of cu, zn and
reducing the copper oxides in situ to form the active catalyst.
2. The process as claimed in claim 1, wherein the said step of co-precipitation comprises:
watering the alumina sol to a temperature of about 70°C
adding the nitrates of copper, zinc, and magnesium,
adding Potassium carbonate in a separate vessel under stirring to allow metals to co-
precipitate.
3. The process as claimed in claim 1, wherein the preferred temperature for ageing is 130°C.
4. The process as claimed in claim 1, wherein the temperature of drying is preferrably
110°C for 3 hrs.

5. The process as claimed in claim 1, wherein the step of calcinate is preferred between
300°C to l000°C.
6. The process as claimed in claim 1, wherein the step of calcination is preferred preferably
at 350°C for 3.5 hrs.
7. The method as claimed in claim 2 wherein the time for precipitation can vary anytime
between 20 min and 4 hours.
8. The method as claimed in claim 3 wherein the time for the aging process can vary
anytime between 1 hour and 10 hours.
9. The method as claimed in claim 1 wherein a ball milling step is added after the
calcination process for deagglomeration of particles during calcination step.
10. The method as claimed in claim 9 wherein the ball milling time can vary between 1 hour
and 10 hours.